" 

* 


0J" 


PRESENTED  TO 

The  UNIVERSITY  of  MLrailil 


EDMONI)  J,  GOOLD. 


G  "FG8UTM.Ce.Tt  BROACW*Y 


WONDERS 


OF   THE 


HUMAN     BODY. 


PROM    THE    FRENCH    OF 


A.    LE    PILEUR,- 


DOCTOR    OF    MEDICINE. 


ILLUSTRATED    BY 
FORTY-FIVE    ENGRAVINGS    BY    LEVEILLE, 


NEW  YORK: 

CHARLES  SCRIBNER  AND  CO. 
187  i. 


3  BIOLOGY 

V 


Illustrated  library  of  Wonders. 


PUBLISHED    BY 


654  BROADWAY,  NEW  YORK. 
Each  one  volume  12mo,  Price  per  volume,  $1.50. 


Titles  of  Books.  No.  of  Illustrations 

THUNDER  AND  LIGHTNING,       .......        39 

WONDERS  OF  OPTICS,         .  TO 

WONDERS  OP  HEAT,       ......  .90 

INTELLIGENCE  OP  ANIMALS,  ... 

GKEAT  HUNTS,     .  .  .  .22 

EGYPT  3,300  YEARS  AGO,     .....  40 

WONDERS  OP  POMPEII,  .  .  .22 

THE  SUN,  BY  A.  GUILLEMIN,         .  ...  53 

SUBLIME  IN  NATURE,     .....  .50 

WONDERS  OP  GLASS- MAKING,       .  ...  63 

WONDERS  OP  ITALIAN  ART,     . »        .  .  .  .  .  .28 

WONDERS  OP  THE  HUMAN  BODY,  .  45 

WONDERS  OP  ARCHITECTURE,  .  .  .50 

LIGHTHOUSES  AND  LIGHTSHIPS,     ......  60 

BOTTOM  OP  THE  OCEAN,  ......      6S 

WONDERS  OP  BODILY  STRENGTH  AND  SKILL,  .  .  TO 

WONDERFUL  BALLOON  ASCENTS,       ...  .30 

ACOUSTICS,     .........         114 

WONDERS  OP  THE  HEAVENS,    .......      48 

THE  MOON,  BY  A.  GUILLEMIN.          .  ...  60 

WONDERS  OP  SCULPTURE         .  .  ....      61 

WONDERS  OP  ENGRAVING,  .....  ->'2 

WONDERS  OP  VEGETATION,      ....  45 

WONDERS  OP  THE  INVISIBLE  WORLD,         .....  97 

CELEBRATED  ESCAPES,  ......  26 

WATER.  .......  ,77 

HYDRAULICS  ....  ...      40 

ELECTRICITY,  .......  71 

SUBTERRANEAN  WORLD,          ....  27 

*  In  Press  fur  early  Publication. 


ITie  above  work*  sent  to  any  address, postpaid,   upon,   receipt  of  the  price  by   the 
publishers. 


PUBLISHERS'    PREFACE. 


THERE  is  an  increasing  tendency  in  the  present  day  to  make 
common  property  of  special  knowledge.  Even  such  infor- 
mation as  formerly  belonged  to  certain  professions  alone  is, 
at  least  in  its  rudiments,  becoming  more  generally  diffused; 
and  on  the  part  even  of  those  professions  the  tendency  is 
recognized  as  within  reasonable  bounds  deserving  of  encour- 
agement. 

To  take  "the  human  body"  as  an  illustration,  medical 
men  find  that  the  useful  feature  of  their  art  is  facilitated  by 
the  dissemination  of  information  regarding  its  structure  and 
functions.  On  the  other  hand,  the  public  daily  see  more  and 
more  clearly  that  "  prevention  is  better  than  cure,"  and  that 
to  prevent  derangements  of  the  wonderful  machine,  with  the 
guidance  of  which  each  individual  is  intrusted,  more  ac- 
quaintance with  its  mechanism  and  laws  of  normal  action 
is  indispensable.  Apart  from  its  utility,  a  knowledge  of 

\  anatomy  and  physiology  is  gradually  becoming  a  necessary 

:  part  of  a  liberal  education. 

To  meet  these  requirements  the  Publishers  now  present 
this  translation  from  the  French  of  a  book  which,  in  the 
original,  has  attained  to  great  popularity.  While  sufficiently 


VI  PREFACE. 

minute  in  anatomical  and  physiological  details  to  satisfy 
those  who  desire  to  go  deeper  into  such  studies  than 
many  may  deem  necessary,  this  work  is  nevertheless  written 
so  that  it  may  form  part  of  the  domestic  library.  Mothers 
and  daughters  may  read  it  without  being  repelled  or 
shocked;  and  the  young  will  find  their  interest  sustained 
by  incidental  digressions  to  more  attractive  matters.  Such 
are  the  pages  referring  to  phrenology  and  to  music,  which 
accompany  the  anatomical  description  of  the  skull  and  of 
the  organs  of  voice;  and  the  chapter  on  artistic  expression 
which  closes  the  book. 

Attention  may  also  be  directed  to  the  numerous  accurate 
and  also  simple  engravings,  which  have  been  introduced  in 
the  hope  of  elucidating  the  verbal  descriptions  in  the  text. 


CONTENTS. 


CHAPTER  I. 

PAGE 

Introduction. — Opinions  of  the  ancients  concerning  the  human 
body. — Summary  of  general  anatomy. — Substance  of  the  body  or 
organized  matter. — Anatomical  elements. — Nutrition.— Fluids. 
— Tissues, I 

CHAPTER  II. 

Form  of  the  body.— Its  beauty. — The  master-pieces  which  it  has 
inspired. — Description  of  the  skin — its  functions, 13 

CHAPTER  III. 

Structure  of  the  body. — Bones,  cartilages,  joints. — Muscles,  ten- 
dons, aponeuroses, 25 

CHAPTER  IV. 

Spinal  column. -^Thorax.  — Upper  limb;  shoulder,  arm,  fore-arm, 
hand. — Lower  limb;  hip,  thigh,  leg,  foot, 41 

CHAPTER  V. 

Motion. — Effort.—  Locomotion;  standing,  walking,  running,  jump- 
ing, swimming, 57 

CHAPTER  VI. 

The  head. — The  skull,  bones  of  the  skull,  sutures,  arch  of  thc 
skull,  base  of  the  skull. — Measurement  of  the  skull;  facial  angle, 
angle  of  Daubenton;  comparison  of  the  superficies  of  the  skull 
and  of  the  face. — System  of  Gall. — The  face,  bones  of  the  face, 
upper  jaw,  lower  jaw, 67 

CHAPTER  VII. 

Digestion. — Waste  of  the  organism  repaired  by  alimentation. — 
Hunger. — Thirst. — Organs  of  digestion;  abdominal  cavity,  peri- 
toneum. —  Digestive  apparatus.  —  Mouth,  lips,  cheeks,  teeth, 
palate,  soft  palate,  tongue. — Pharynx. — (Esophagus. — Stomach. 
— Intestinal  canal;  small  intestine,  large  intestine,  intestinal  con- 


Vlll  CONTENTS. 

PAGE 

volutions,  mesentery,  omen  turn. — Mucous  membrane. — Liver. — 
Pancreas. — Spleen. — Kidneys. — Mechanism  of  digestion. — Di- 
gestion of  the  stomach,  gastric  juice,  peristaltic  movement,  chyme. 
— Intestinal  digestion,  bile,  pancreatic  juice,  chyle. — Absorption; 
endosmosis,  exosmosis,  functions  of  the  veins  and  lymphatic 
vessels  in  absorption,  rapidity  of  absorption, 73 

CHAPTER  VIII. 

Respiration. — Thoracic  cavity;  pleura. — Organs  of  respiration: 
lungs,  trachea,  bronchia. — Respiration;  influence  of  respiration 
on  the  blood,  Lavoisier's  theory,  theory  of  catalytic  phenomena; 
mechanism  of  respiration,  respiratory  sounds,  frequency  of  re- 
spiration; capacity  of  the  lungs;  modification  of  the  air  in  the 
lungs. — Influence  of  atmospheric  pressure.  6n  respiration;  moun- 
tain-sickness,   89 

CHAPTER  IX. 

Circulation. — Organs  of  the  circulation;  heart,  pericardium;  arteries, 
capillaries,  principal  arteries;  veins,  principal  veins;  portal  sys- 
tem; lymphatic  vessels  and  ganglia. — Mechanism  of  the  circula- 
tion; discovery  of  the  circulation,  action  and  sounds  of  the  heart, 
arterial  circulation,  pulse,  capillary  circulation;  venous  circula- 
tion, valves  of  the  veins;  discharge  of  chyle  and  lymph  into  the 
veins.  Sanguification;  circulation  in  the  pulmonary  artery, 
capillaries,  and  pulmonary  veins. — Influences  which  accelerate  or 
retard  the  beating  of  the  heart, IO2 

CHAPTER  X. 

Nervous  system. — Cerebro-spinal  nervous  centre.  —  Cerebrum. — 
Cerebellum. -^-Isthmus  of  the  encephalon. — Medulla  oblongata. — - 
Spinal  cord. — Membranes;  dura  mater,  arachnoid,  pia  mater. — 
Nerves;  cranial  nerves,  spinal  nerves,  great  sympathetic. — Func- 
tions of  the  nervous  system;  functions  of  the  spinal  nerves  of 
motion  and  of  sensation;  function  of  the  cranial  nerves;  functions 
of  the  spinal  marrow. — Functions  of  the  encephalon;  medulla 
oblongata,  pons  Varolii,  peduncles  of  the  cerebrum  and  cere- 
bellum, corpora  quadrigemina,  pineal  gland,  optic  thalami, 
cerebrum  and  cerebellum. — Functions  of  the  great  sympathetic. 
— Reflex  power. — Nerve  force.— Memory, 119 

CHAPTER   XI. 

Sense  of  sight. — Organ  of  vision.— Globe  of  the  eye;  sclerotic; 
cornea;  choroid  ;  ciliary  ring;  ciliary  body  ;  ciliary  process;  iris; 

Eupil ;    uvea;   pigment;    retina;   vitreous   body;   hyaloid    mem- 
rane ;    crystalline ;    anterior  and  posterior  chambers ;    aqueous 
humour. — Muscles  of  the  eye. — Conjunctiva. — Eyelids,  eyelashes. 


CONTENTS.  ,  IX 

PAGE 

— Lachrymal  apparatus. — Vision;  functions  of  the  retina,  .re- 
versed images ;  functions  of  the  iris ;  optic  centre,  visual  angle, 
visual  impressions,  single  or  mixed,  adaptation  of  the  eye  to  dis- 
tances, myopia,  presbyopia ;  achromatism ;  single  and  double 
vision  with  two  eyes,  stereoscope;  alternation  in  the  action  of 
the  eyes ;  persistence  of  impressions  on  the  retina ;  accidental 
images  ;  irradiation  ;  accidental  aureola ;  Daltonism ;  apparent 
motion  of  objects! — Optic  nerve. — Movements  of  the  eye. — Ex- 
tent of  vision, 152 

CHAPTER    XII. 

Sense  of  hearing. — Organ  of  hearing. — External  ear;  pavilion  of 
the  ear,  auditory  canal. — Middle  ear;  tympanum,  drum,  or 
membrana  tympani,  fenestra  ovalis,  fenestra  rotunda,  Eustachian 
tube,  the  small  bones  of  the  ear,  muscles  and  movements  of  the 
small  bones. — Internal  ear;  labyrinth,  vestibule,  semicircular 
canals,  cochlea,  membranous  labyrinth. — Auditory  nerve. — 
Noises  and  sounds;  duration,  pitch,  intensity  and  quality  of 
sound ;  passage  of  sound  through  air,  water,  solid  bodies ; 
gravity,  sharpness  of  sound. — Mechanism  of  hearing;  functions 
of  different  parts  of  the  ear;  movement  of  sounds  in  the  ear; 
propagation  of  sounds  to  the  auditory  apparatus  by  the  vibrations 
of  the  bones  of  the  skull. — Opinions  of  physiologists  on  the 
functions  of  different  portions  of  the  labyrinth ;  theory  of  Helm- 
holtz. — Fineness  and  delicacy  of  hearing. — Correctness  of  the 
ear. — Estimation  of  the  intensity,  the  distance,  and  the  direction 
of  sounds;  ventriloquism. — Duration  of  auditory  impressions. — 
Sensations  having  an  internal  origin. — Parallel  between  the  eye 
and  ear, 182 

CHAPTER   XIII. 

Sense  of  smell.  Olfactory  organs. — Nose;  nasal  fossae,  turbinated 
bones,  pituitary  membrane.  —  Olfactory  nerve.  Odoriferous 
principles ;  their  development,  their  action  on  the  nervous  sys- 
tem.— Smell, — its  seat ;  duration  of  olfactory  impressions. — Uses, 
and  acuteness  of  smell,  203 

CHAPTER   XIV. 

Sense  of  taste. — Organ  of  taste. — Special  nerves  of  the  organ. — 
Flavours. — Taste, 210 

CHAPTER    XV. 

Sense  of  touch. — Difference  between  touch  and  feeling. — Tactile 
sensibility  and  general  sensibility. — Organ  of  touch.  Sensation 
of  contact ;  difference  in  the  sensibility  of  different  regions  of  the 
body;  simple  contact,  shock,  vibration. — Sensation  of  pressure; 


X  CONTENTS. 

PAGE 

relative  aptitude  of  different  regions  in  appreciating  it;  \ariable 
sensation  according  to  the  form  of  the  body  and  the  extent  of 
its  surface. — Sensation  of  temperature,  variable  according  to  the 
temperature  of  the  skin,  the  density  of  bodies,  and  the  surface  in 
contact ;  identical  sensation  from  contact  with  a  body  very  hot 
and  very  cold ;  relative  sensibility  of  different  regions  to  tem- 
perature.— The  touch;  its  delicacy. — The  touch  compared  with 
the  other  senses ;  illusions  of  touch ;  persistence  of  tactile  impres- 
sions, sensations  from  internal  or  subjective  causes ;  causes  which 
modify  feeling, .217 

CHAPTER    XVI. 

Voice  and  speech. — Organ  of  voice;  larynx,  cavity  of  the  larynx, 
glottis,  vocal  cords ;  the  larynx  at  different  ages  and  in  different 
sexes.  — Physiology  of  the  larynx ;  mechanism  of  the  voice ; 
opinions  as  to  the  formation  of  the  voice. — Galen,  Fabricius 
Acquapendente,  Dodart,  Ferrein,  Biot,  Miiller,  Savart,  Masson, 
and  Longet. — Theories  founded  on  laryngoscopic  observations. — 
Formation  of  sounds  in  whistling. — Voice;  speaking  voice, 
mechanism  of  articulate  sounds,  vowels,  consonants,  timbre  of  the 
vowels;  the  tongue  as  an  organ  of  pronunciation. — Singing; 
chest  voice,  falsetto  voice,  mixed  voice ;  different  theories  on  the 
formation  of  the  falsetto :  Miiller,  M.  Segond,  M.  Longet,  M. 
Fournie,  M.  Bataille,  M.  Mandl. — Timbres  of  the  voice :  high 
pitch,  grave  pitch. — Compass  of  voices:  bass,  baritone,  tenor, 
contralto,  mezzo-soprano,  soprano. — Ventriloquy, 228 

CHAPTER   XVII. 

Physiognomy ;  study  of  it  in  works  of  art. — Movements  of  expres- 
sion, their  seat. — Colouring  of  the  skin ;  paleness,  redness. — Ex- 
pression of  the  muscles;  effort,  muscles  of  the  face. — Physiognomy 
of  the  senses. — Expression  of  the  eyes,  vision,  easy  or  difficult, 
blindness. — Expression  in  the  act  of  hearing,  easy  or  difficult, 
hearing  of  an  orator,  musical  hearing. — Expressions  of  smell  and 
taste. — Expressions  relating  to  the  touch 247 


LIST    OF    ILLUSTRATIONS. 


FIG.  rAG3 

1.  Blood  seen  under  the  microscope, 4 

2.  Bony  tissue  as  seen  with  the  naked  eye, 8 

3.  Osseous  and  cartilaginous  tissues  as  seen  through  the  micro- 

scope,       8 

4.  Laminated  fibres  in  the  first  stage  of  development,    ....  9 

5.  Stripped  muscular  tissue  as  seen  under  the  microscope,       .      .  10 

6.  Nervous  tissue  seen  under  the  microscope, 1 1 

7.  A  nerve  and  its  ramifications  seen  by  the  naked  eye,     ...  12 

8.  Apollo  Belvedere, 15 

9.  The  Venus  of  Milo, 17 

10.  The  Skin, 21 

11.  Skeleton, 27 

12.  Elbow-joint, 33 

1 3.  Biceps  muscle  of  the  arm, 35 

14.  Lower  portion  of  the  leg, 37 

15.  The  hand,  palmar  aspect, 46 

1 6.  The  hand,  dorsal  aspect, 46 

17.  Knee-joint, 52 

1 8.  Skeleton  of  the  foot, 54 

19.  The  foot, 55 

20.  The  leg  in  standing, 61 

21.  Section  of  the  trunk  and  its  cavities  in  the  median  line,      .  74 

22.  Section  in  the  median  line  through  the  inferior  portion  of  the 

nasal  fossne,  the  mouth,   pharynx,  larynx,  oesophagus,  and 

trachea, /6 

23..  Transverse  section  of  the  thoracic  and  abdominal  cavities,       .  Si 

24.    Lungs  and  heart, 91 


Xll  LIST    OF    ILLUSTRATIONS. 

FIG.  PAGE 

25.  Section  showing  the  ramifications  of  the  bronchi  in  the  lungs,  93 

26.  Heart  and  principal  arterial  and  venous  trunks, 103 

27.  Transverse  section  of  the  heart, 105 

28.  Imaginary  diagram  of  the  course  of  the  blood  in  the  circula- 

tion,    116 

29.  Cerebro-spinal  nervous  centre, 120 

30.  Nervous  system, 121 

31.  Upper  surface  of  the  brain, 123 

32.  Lower  surface  of  the  brain, •  .  124 

33.  Section  of  the  encephalon  in  the  median  line, 126 

34.  Vertical  section  of  the  eye  on  the  median  line, 153 

35.  Rods  of  Jacob  under  the  microscope, 156 

36.  Diagram  illustrating  "blind  point "  in  retina, 161 

37.  Course  of  the  luminous  rays  in  the  eye, 162 

38.  Diagram  illustrating  the  visual  angle, 164 

39.  Accommodation  of  the  eye  to  different  distances,      .      .     .      .  167 

40.  Diagram  illustrating  single  vision  with  two  eyes,       .      .     .     .  1 70 

41.  Irradiation, 176 

42.  Section  showing  the  different  parts  of  the  ear, 183 

43.  Experiment  on  the  sensations  of  touch, 226 

44.  Section  of  larynx  in  the  median  line, 229 

45.  The  glottis  and  vocal  cords, 242 


THE 


HUMAN     BODY. 


CHAPTER    I. 


INTRODUCTION. 

Opinions  of  the  ancients  concerning  the  human  body. — Summary  of  general 
anatomy. — Substance  of  the  body  or  organized  ?natler. — Anatomical 
elements.  — Nutrition.  — Fluids.  —  Tissues. 

IT  has  been  said  with  truth,  that  the  human  mind,  which 
can  survey  the  heavens  and  calculate  the  motion  and  density 
of  the  stars,  finds  itself  confounded  when,  returning  from 
these  distant  journeyings,  it  enters  its  own  proper  dwelling- 
place.  Man's  own  organization  is  still  among  those  mysteries 
of  nature  which  he  is  least  able  to  penetrate,  in  spite  of  his 
incessant  efforts  to  lift  the  veil  which  hides  it.  In  all  ages 
he  has  sought  to  know  himself;  in  all  times  he  has  studied 
the  relations  between  his  own  existence  and  that  of  the 
world;  and  those  universal  influences  which,  though  evident 
to  him,  are  nearly  all  inexplicable  in  their  action  upon  living 
beings. 

Carried  by  their  imagination  into  this  way  of  comparing 
the  human  body  with  the  rest  of  creation,  Aristotle  and  some 
other  philosophers  saw  in  man  an  epitome  of  the  wonders 
of  the  universe.  He  was  for  them  the  microcosm,  the  dimi- 
nutive and  summary  of  the  entire  world. 

Paracelsus  and  the  astrological  doctors  developed  from 
their  stand-point  the  ideas  of  the  Greek  philosophers,  and 
pushed  to  its  extreme  limits  the  doctrine  of  sidereal  influence 


2  THE    HUMAN    BODY. 

upon  man.  According  to  them,  the  body  had,  like  the  earth, 
an  axis  and  two  poles ;  the  head,  the  seat  of  the  soul,  corres- 
ponded to  the  heavens  where  divinity  resided,  &c. 

Since  that  time,  and  especially  in  our  own  day,  the  ima- 
gination has  given  way  to  a  rigorous  method  of  study  and 
to  positive  ideas.  But  whether  we  venturously  follow  Aris- 
totle and  Paracelsus,  or  whether  we  prefer  the  exact  results 
of  science  to  their  poetic  theories,  we  shall  always  see  in 
the  human  body  the  highest  and  most  perfect  creation  of 
nature  among  living  beings,  and  we  shall  admire  the  efforts 
and  the  discoveries  which  the  study  of  its  organization  has 
enabled  the  mind  to  make  from  the  time  of  the  masters  of 
antiquity  down  to  our  own  day. 

In  the  human  body,  as  in  animals  and  in  the  vegetable 
kingdom,  the  organized  matter  is  composed  of  what  are 
termed  proximate  (or  immediate)  principles  and  anatomical 
elements.  Of  these  proximate  principles  some  are  of  mineral 
origin,  as  oxygen,  water,  the  carbonates,  the  chlorides,  the 
phosphates,  &c.  They  penetrate  the  organism,  and  there 
furnish  the  materials,  by  the  aid  of  which  other  principles  of 
a  different  order  are  formed.  These  last  essentially  consti- 
tute the  body,  hence  the  name  organic  substances  is  specially 
applied  to  them.  There  is  nothing  in  the  mineral  kingdom 
analogous  to  these  organic  substances,  though  they  borrow 
their  original  elements  from  it.  They  are  solid  or  semi-solid 
(globuline,  musculine),  liquid  or  semi-liquid  (fibrine,  albu- 
men, caseine),  colouring  or  coloured  (hematosine,  biliver- 
dine).  They  decompose  where  they  are  formed,  and  give 
birth  to  another  class  of  proximate  principles.  These  last 
are  of  very  different  natures,  and  possess  different  attributes; 
they  are  acids,  salts,  alkaloids,  fatty  bodies;  they  are  urea, 
creatine,  stearine,  cholesterine,  and  the  sugar  of  the  milk 
and  of  the  liver,  lactic  acid,  uric  acid,  &c. 

This  double  and  continuous  movement  of  combination 
and  resolution  of  proximate  principles  results  in  the  forma- 
tion of  the  anatomical  elements.  This  is  the  term  applied  to 
very  minute  bodies,  free  or  attached,  which  present  special 
geometrical,  physical,  and  chemical  characters,  as  well  as  a 
structure  which  has  no  analogy  to  that  of  minerals. — They 


NUTRITION — HUMOURS.  j 

are  the  smallest  organic  subdivisions  of  which  the  tissues 
and  fluids  are  capable  by  anatomical  analysis.  Their  reunion 
and  combination  form  the  solids  and  liquids  of  the  organism. 
By  assimilation  they  borrow  their  substance  from  the 
molecules  of  the  proximate  principles,  while  at  the  same 
time  and  in  equal  proportions  they  abandon  other  molecules 
of  these  same  principles  by  a  process  of  separation. 

This  assemblage  of  phenomena  is  termed  nutrition.  In 
this  manner  water,  carbon,  lime,  phosphorus,  iron,  and  the 
other  principles,  co-operate  in  forming  globuline,  fibrine, 
musculine,  and  the  other  organic  substances,  which  by  their 
combination  constitute  the  anatomical  elements  of  the  blood, 
the  muscles,  the  bones,  the  nerves,  the  body  in  a  word;  this 
is  assimilation. 

At  the  same  time  other  molecules  of  the  same  principles, 
in  equal  proportions,  abandon  by  a  separatory  process  the 
substance  of  the  organism,  and  unite  to  form  the  milk, 
saliva,  tears,  bile,  and  the  other  secretions,  which  are  to  be 
completely  excreted  as  improper  for  nutrition,  or  partially 
thrown  oft  and  partially  returned  to  the  system. 

As  to  the  anatomical  elements,  some  of  them  have  a  form 
which  may  be  described,  as  globule,  fibre,  tube,  and  cell; 
others  are  amorphous,  and  serve  to  fill  the  spaces  between 
those  first-named. 

We  see  therefore  that  the  immediate  or  proximate  prin- 
ciples and  the  anatomical  elements  constitute  all  organized 
matter  whether  solid  or  fluid. 

The  fluid  portions  of  the  human  body  greatly  exceed  the 
solid ;  they  are  computed  at  nine-tenths  of  the  whole  weight. 
Water  enters  largely  into  the  composition  of  these  fluids, 
a  portion  of  which  only  is  contained  in  the  vessels  or 
reservoirs  specially  set  apart  for  each  of  them,  while  the 
remainder  penetrates  the  solid  parts  and  forms  part  of  their 
substance. 

The  term  humours — fluids— is  applied  to  the  liquid  or 
semi-liquid  portions  of  the  organism  formed  by  the  mingling 
and  dissolution  of  immediate  principles,  and  they  ordinarily 
hold  the  anatomical  elements  in  suspension.  The  solid 
portions  are  called  tissues. 


4  THE    HUMAN    BODY. 

These  fluids  are  classed,  according  to  the  part  they  play  in 
the  human  economy,  into  constituent  fluids,  secreted  fluids 
or  secretions,  excretions,  and  intermediate  products,  which 
partake  of  the  nature  of  the  other  three.  The  constituent 
fluids  are  three  in  number — the  blood,  chyle,  and  lymph. 
The  blood  is  the  nutritive  fluid  of  the  body;  it  contains  all 
the  immediate  principles  that  are  found  in  its  organism.  In- 
cessantly renewed  by  digestion  and  respiration,  it  supplies 
to  each  organ  assimilable  matter,  and  to  the  special  labora- 
tories the  materials  for  the  secretions,  and  carries  off  the 
results  of  disassimilation  which  are  to  be  thrown  out  of  the 
organism.  It  is  therefore  at  once  a  reparative  and  a  purify- 
ing fluid.  The  term  "  fluid  flesh,"  which  has  been  applied 


Fig.  i.— Blood  seen  under  the  microscope. 

to  it,  is  incomplete,  for  it  contains  not  only  the  muscular 
tissue,  but  the  essential  elements  of  all  the  other  tissues  are 
found  in  its  mass. 

The  blood  is  heavier  than  water,  its  specific  gravity  being 
1052  to  1057,  while  that  of  water  is  1000.  In  the  blood- 
vessels the  blood  is  composed  of — ist.  anatomical  elements, 
red  and  white  corpuscles.  2d.  Of  a  fluid,  of  which  779  parts 
in  weight  in  1000  are  water  in  men,  and  in  women  791 
parts  in  1000.  This  fluid  is  the  plasma,  the  plastic  substance, 
the  nourishing  juice  in  which  are  found  all  the  immediate 


BLOOD,  g 

principles  of  the  blood.  Among  these,  principles  are  lime, 
ammonia,  soda,  potash,  phosphorus,  magnesia,  iron  and  other 
metals  in  the  form  of  salts;  chlorides,  sulphates,  carbonates, 
phosphates,  &c.;  and  mingled  with  these  are  the  principles 
of  the  secretions  and  organic  substances,  of  which  the  most 
important,  from  their  quantity,  are — fibrine,  2-5  parts  in  1000, 
and  albumen  69  to  70  in  1000. 

The  blood  owes  its  colour  to  the  red  corpuscles,  which  are 
themselves  coloured  by  a  substance  which  De  Blainville  has 
named  hematosine,  and  which  contains  7  parts  in  i  oo  of  iron. 
These  corpuscles  are  round  flattened  disks  of  *oo6  to  '007 
of  a  millimetre  in  diameter,  and  a  thickness  of  '002  milli- 
metre. Under  the  microscope  they  appear  grouped  together 
without  order,  or  piled  one  upon  another  like  pieces  of 
money,  and  are  of  a  red  colour  in  reflected  light.  The  white 
corpuscles  are  smooth,  spherical,  of  a  yellowish-white  colour 
in  a  reflected  light,  and  from  '008  to  "014  of  a  millimetre  in 
diameter. 

The  colour  of  the  blood  is  a  beautiful  crimson  red  in  the 
arteries,  but  of  a  darker  colour  in  the  veins.  We  shall  have 
occasion  to  examine  it  from  this  point  of  view  in  treating  of 
the  circulation. 

When  blood  which  has  been  drawn  is  allowed  to  stand  in 
the  vessel,  it  separates  into  two  distinct  parts :  the  one,  semi- 
solid,  is  called  the  crassamentum— the  clot;  the  other  fluid, 
is  called  serum.  The  clot  is  the  coagulated  fibrine  which 
carries  with  it  the  red  globules  which  were  held  in  suspension 
in  the  blood.  When  the  coagulation  is  delayed,  these  glob- 
ules, being  heavier  than  the  other  portions  of  the  blood,  fall 
toward  the  lower  part  of  the  vessel;  and  the  fibrine,  freed 
from  them,  coagulates  and  retains  its  own  proper  colour,  and 
the  clot  is  composed  of  two  layers — the  superficial  layer  is 
of  a  grayish  or  white  colour  and  semi-transparent,  and  is 
termed  the  "buffy  coat."  It  is  formed  of  pure  fibrine  mingled 
with  the  white  globules;  the  other  is  composed  of  fibrine  and 
of  the  red  globules  which  give  it  its  colour.  The  serum 
is  a  transparent,  greenish-yellow  fluid,  sometimes  a  little 
whitened  by  minute  fatty  specks;  from  which  circumstance, 
and  from  some  other  points  of  analogy  between  them,  it  has 


6  THE    HUMAN    BODY. 

been  called  the  whey.  It  is  a  little  less  dense  than  the  clot, 
and  contains  among  other  principles  a  great  deal  of  albumen. 
The  serum  is  the  plasma  without  the  fibrine. 

The  chyle  is  a  white  opaque  fluid  closely  resembling  milk, 
which  is  separated  from  the  food  during  the  process  of  diges- 
tion, and  is  drawn  by  the  chyliferous  vessels  from  the  surface 
of  the  smaller  intestine,  and  serves  to  form  the  blood.  As 
it  advances  toward  the  point  where  it  mingles  with  the  blood, 
it  resembles  this  fluid  more  and  more  in  its  composition;  it 
takes  a  roseate  tint,  and,  if  left  to  itself,  it  separates  into 
fibrinous  clot  and  albuminous  serum. 

The  lymph  is  a  clear,  transparent  fluid,  slightly  tinted  with 
green  or  yellow.  Drawn  from  the  organs  by  the  lymph- 
atic vessels,  and  especially  from  the  skin  and  the  surface 
of  the  mucous  and  serous  membranes,  the  lymph  is  poured 
into  the  mass  of  blood  by  two  principal  canals.  Like 
the  chyle  it  contains  white  globules  and  minute  specks  of 
fat.  When  extracted  from  the  lymphatic  vessels,  it  also 
separates  into  fibrinous  clot  and  serum,  containing  a  little 
albumen. 

We  see  therefore  that  chyle  and  lymph  are  imperfect  blood. 
The  chyle  leaves  the  digestive  apparatus  in  a  crude  state,  and 
goes  to  the  blood-making  laboratories  for  its  perfection.  The 
lymph  comes  from  the  extreme  limits  of  the  organs  to  these 
same  laboratories,  and,  uniting  with  the  chyle,  is  poured  into 
the  blood — the  constituent  fluid  par  excellence. 

The  secreted  fluids  or  secretions  are  produced  by  special 
apparatus  from  the  materials  furnished  by  the  constituent 
fluids.  They  differ  from  these  last  in  being  only  a  medium 
for  the  elements  which  they  hold  in  suspension,  these  elements 
not  being  essential  to  them,  as  the  globules  are  to  the  blood, 
for  example.  They  all  contain  one  or  several  organic  fluid 
substances,  to  the  nature  of  which  the  secreted  fluid  owes  its 
essential  properties.  These  humours  are  very  numerous,  and 
play  a  very  distinct  part  in  the  human  economy.  They  are 
normal  or  morbid,  as  they  owe  their  origin  to  the  regular 
function  of  the  organs  or  are  modified  by  the  action  of  disease. 
We  shall  mention  only  milk,  which  resembles  the  blood  by 
composed  largely  of  serum,  and  which  cannot  be 


CHYME — TISSUES.  7 

replaced  by  any  substance  for  the  alimentation  in  the  first 
stages  of  infancy; — the  aqueous  and  vitreous  humours  of  the 
eye,  the  synovia  which  bathes  and  lubricates  articulated  sur- 
faces, the  tears,  and  the  saliva,  which  we  shall  see  later  takes  a 
part  in  digestion,  and  in  which  Mons.  Longet  has  shown  the 
existence  of  minute  and  therefore  harmless  proportions  of 
sulpha-cyanide  of  potassium,  one  of  the  most  virulent  poisons. 
In  popular  language  the  term  humour  is  applied  exclusively 
to  the  purulent  fluids,  morbid  products  which  differ  in  some 
particulars  according  to  the  conditions  under  and  the  organs 
in  which  they  are  formed.  It  is  unfortunate  that  they 
should  monopolize  a  term  which  belongs  to  all  the  organic 
fluids. 

We  shall  merely  point  out  the  intermediate  products,  among 
which  figures  the  chyme,  a  semi  fluid  substance  formed  in  the 
stomach  during  digestion,  and  the  excretions  which  the  system 
rejects,  after  having  separated  from  them  nearly  all  assimil- 
able principles. 

The  tissues  are  the  solid  parts  of  the  body,  formed  of 
anatomical  elements  either  bound  together  or  simply  in 
juxtaposition.  The  tissues  are  classed  according  to  the 
elements  peculiar  to  them,  according  to  their  texture,  that 
is  to  say  the  mode  in  which  these  elements  are  arranged; 
and  according  to  their  essential  properties,  which  are  either 
physico-chemical,  such  as  consistence,  extensibility,  retrac- 
tility, elasticity,  and  hygrometricity,  or  organic,  like  the 
properties  of  absorption,  of  secretion,  of  development,  of 
regeneration,  of  contractility,  and  of  innervation.  These 
properties  are  variable  according  to  the  tissues,  which  are 
more  or  less  tenacious,  more  or  less  extensible,  and  so  forth. 
Or  they  are  peculiar  to  certain  tissues,  and  independent,  for 
a  tissue  may  be  retractile  and  not  extensible  or  elastic,  and 
vice  versa.  Constituent  tissues  are  those  which,  composed 
of  the  fundamental  elements,  fibre,  cell,  and  tube,  form  the 
essential  organism.  Produced  tissues  are  those  which  eman- 
ate from  the  first,  and  may  be  detached  from  them  without 
destroying  them,  and  are  only  accessory  or  complementary 
parts.  These  products  are  normal  or  morbid,  according  to 
their  nature  and  substance. 


THE    HUMAN    BODY. 


Air.ong  the  numerous  tissues  which  exist  in  the  economy 
we  cite  the  following: — 


Fig.  2. — Bony  tissue  as  seen  with  the  naked  eye. 


Fig-  3- — Osseous  and  cartilaginous  tissues  as  seen  through  the  microscope. 

A,  Cells  of  cartilaginous  tissue. 

B,  Section  of  a  canal  of  Havers,  showing  the  disposition  of  the  s  tarty 

cells  in  the  substance  of  a  bone. 

C,  Starry  cells  magnified. 


Osseous  or  bony  tissue,  which  is  composed  principally  of 
an  anatomical  element  called  osteoplasm.     It  is  compact  in 


CELLULAR,    ADIPOSE,    MUSCULAR    TISSUE. 


some  parts  of  the  bones,  and  spongy  in  others.  This  tissue 
is  traversed  by  infinitely  ramified  conduits,  called  the  canals 
of  Havers,  which  contain  the  blood-vessels  and  the  medullary 
substance  or  marrow. 

Cartilaginous  and  fibre-cartilaginous  tissue. 

Cellular  or  connective  tissue,  more  exactly  named  laminated 
tissue,  formed  of  laminated  fibres,  long,  flattened,  undulated 
filaments  in  bundles,  and  of  fibres  appertaining  to  elastic 
tissue.  In  nearly  every  part  of  the  body  this  substance  fills 
the  spaces  between  the  tissues  or  between  the  bundles  of  the 
fibres  of  which  they  are  made  up :  on  the  surface  of  the  body 
and  of  its  cavities,  and  around  the  organs,  it  is  disposed  in 
enveloping  membranes. 

Adipose  tissue  is  formed  of  cells 
or  vesicles  containing  fat.  It  is 
never  found  except  in  the  cellular 
tissue  and  at  the  points  where  this 
last  is  least  dense. 

These  two  tissues  united  are  com- 
monly designated  by  the  term  fat, 
or  fatty  layer,  but  they  are  distinct 
notwithstanding,  and  neither  wasting 
nor  increase  of  fat  causes  any  change 
in  the  mass  of  the  cellular  tissue,  but 
only  in  the  quantity  of  fat  contained  ,-,. 

•;  "_  J  _.  .  Fig.  4. — Laminated  fibres  in  the 

111  the  Cells  Of  the  adipose  tiSSUe.  first  stage  of  development. 

Epithelial  tissue  has  for  its  ana- 
tomical elements,  cells  or  free  nuclei,  which  form  by  juxta- 
position either  a  very  thin  single  layer,  or  several  superposed 
layers.  It  is  of  this  tissue  that  the  epidermis  and  the 
epithelium,  a  kind  of  internal  epidermis,  are  essentially  com- 
posed. 

Muscular  tissue.  This  constitutes  the  muscles,  or.  the 
flesh,  properly  speaking.  It  is  composed  of  elements  called 
muscular  fibres,  which  are  of  two  sorts,  the  smooth,  formed 
of  fibre-cells,  and  the  striped,  formed  of  bundles  of  fibrils. 
The  fibrils  are  the  fundamental  element  of  the  muscular 
tissue;  their  primitive  microscopic  bundles  unite  in  secon- 
dary bundles  visible  to  the  naked  eye,  and  are  known  in 


10 


THE    HUMAN    BODY. 


descriptive  anatomy  under  the  name  of  fibres  of  the  muscles. 
The  fibrils  are  contractile  but  not  elastic,  and  their  primitive 
bundles  have  a  homogeneous  envelope  of  elastic  but  not 
contractile  tissue  called  sarcolemma. 

Fibrous  tissue  has  the  same  ele- 
ments as  the  cellular  tissue,  united 
in  compact  bundles  visible  to  the 
naked  eye,  strongly  adherent  among 
themselves,  and  interlaced  in  every 
direction.  Fibrous  tissue  is  found 
especially  in  the  articulating  and  inter- 
osseous  ligaments  and  in  certain  en- 
veloping membranes,  as  the  sclerotic, 
for  example,  which  forms  the  white 
of  the  eye. 

Tendinous  and  aponeurotic  tissue 
is  made  up  of  a  variety  of  very  thin 
laminated  fibres,  with  puckered  edges, 
undulated  and  adhering  directly  at 
one  extremity  to  the  sarcolemma  of 
the  striped  muscular  fascicles,  and  to 
the  osseous  substance  at  the  other. 
These  fibres  unite  in  little  flattened 
polyhedral  bundles,  from  'ooi  to  "002 
of  a  millimetre  in  breadth,  from  which 
the  tendons  and  aponeuroses,  which 
are  of  a  tendinous  nature,  are  formed. 
Tendinous  tissue  is  in  extensible 
lengthwise,  and  inelastic. 

Nervous  tissue  is  essentially  formed 
of  tubes,  which  are  large  and  small. 
They  have  homogeneous,  thin,  trans- 
parent walls,  and  contain  a  viscous, 
fatty  fluid,  which  is  the  medullary  substance  or  the  whitr 
substance  of  Schwann,  in  which  there  is  a  sort  of  stem — the 
axis-cylinder.  In  the  spinal  marrow  and  in  the  brain  the 
walls  of  the  tube  are  wanting,  and  only  the  medullary  sub- 
stance and  the  axis-cylinder  remain.  As  we  approach  the 
outside  of  the  body  we  find,  on  the  contrary,  that  the  tubes 


Fig.  5. — Striped  muscular  tis- 
sue as  seen  under  the 
microscope. 

A,  Fibril  deprived  of  the  sar- 
colemma, to  show  the  disks 
of  which  it  is  composed. 

A',  One  of  these  disks. 

B,  Several  fibres  less  magni- 
fied. 


NERVE-TISSUE. 


II 


become  more  homogeneous  in  structure,  until  at  their  ex- 
tremity they  are  reduced  to  a  filament  in  which  the  walls,  the 


Fig.  6.— Nervous  tissue  seen  under  the  microscope. 

a.  b,  SpJierical  nerve-cells. 

c,  Bi-polar  cell. 
/>,  Multi-polar  cells. 

h,  Cells  of  the  ganglia  and  nen>e-jib*'es. 

i,  Nerve-tube  and  axis-cylinder. 

k,   Termination  of  a  nerve-fibre  in  an  organ. 

cylindrical  axis,  and  medullary  substance  are  not  distinguish- 
able At  certain  points  of  the  nervous  system  the  tubes 
differ  anatomically,  according  as  they  belong  to  the  nerves 
of  sensation  or  the  nerves  of  motion. 

Other  elements  also  are  found  in  the  nervous  tissue — (he 
ganglionic  cells  or  corpuscles*  and  the  fibres  of  Remak. 

The  ganglionic  corpuscles •,  so  called  because  they  are  found 
in  the  substance  of  the  ganglia,  receive  the  sensitive  tubes 
as  they  come  from  the  brain  or  spinal  marrow.  These  tubes 
unite  with  the  walls  of  the  corpuscle  at  one  of  the  points 
or  poles  of  its  periphery,  and  emerge  from  it  at  the  opposite 
pole. 


12 


THE    HUMAN    BODY. 


The  ganglionic  corpuscles  are  divided    into   bi-polar  or 
multi-polar,  according  as  they  receive  one  or  several  tubes. 


Fig.  7.-   A  nerve  and  its  ramifications  seen  by  the  naked  eye. 

The  fibres  of  Remak  appear  to  be  one  of  the  constituent 
elements  of  the  filaments  of  the  nerves  of  motion. 


CHAPTER   IT. 


Form  of  the  body — its  beauty.  —  The  master-pieces  which  it  has  inspired. — 
Description  of  the  skin — its  functions. 


Nature,  in  modelling  animals,  has  marvellously  adapted 
their  forms  to  the  functions  and  to  the  mode  of  life  to  which 
.she  has  destined  them;  but  no  creature  has  received  in  the 
same  degree  as  man,  that  mingling  of  strength  and  of  elegance 
in  contour,  of  grandeur  and  delicacy  in  the  lines,  and  in  no 
other  has  she  taken  such  care  to  distinguish  the  two  sexes  in 
bestowing  upon  them  her  most  precious  gifts.  It  is  of  the 
human  race  alone  that  BufTon  could  say:  "Man  has  strength 
and  majesty;  beauty  and  the  graces  are  the  dowry  of  the 
other  sex." 

The  fabulist,  using  the  poet's  privilege,  makes  the  lion  say — 

''Lions  might  hold  the  upper  hand, 
If  they  but  had  the  art  to  paint." 

Doubtless  in  comparing  himself  with  certain  animals,  man 
cannot  ignore  his  inferiority  in  muscular  strength  and  in  the 
arms  which  nature  has  given  him;  but  what  matters  it?  He 
feels  his  superiority  to  these  beings,  though  they  are  stronger 
and  better  armed  than  he.  He  knows  how  to  avoid  their 
attacks  and  to  triumph  over  their  brute  force.  He  constrains 
them  to  his  service,  and  disposes  of  their  lives  and  of  their 
bodies,  by  obeying  not  a  blind  instinct  but  the  voice  of  reason. 
If  he  believes  himself  first  among  the  dwellers  on  his  planet, 
it  is  not  his  vanity  which  persuades,  but  his  intelligence  that 
proves  it  to  him,  and  gives  him  the  right  to  treat  all  other 
creatures  as  their  master. 

We  admire  the  majestic  bearing  of  a  tree,  the  elegance  of 


14  THE    HUMAN    BODY. 

a  flower,  the  plumage  and  flight  of  a  bird,  the  stately  tread 
of  some  huge  mammal,  but  nothing  impresses  us  so  much 
as  the  human  form.  It  is  not  from  sympathy  with  beings 
of  our  own  species  that  we  find  them  more  beautiful;  the 
judgment  that  we  pronounce  upon  their  beauty  is  not  due 
to  the  inclination  of  one  sex  to  the  other;  this  sympathy  and 
this  inclination  are  common  to  most  of  the  superior  animals, 
but  man  alone  appreciates  the  difference  between  individuals 
as  between  species;  it  belongs  to  him  only  to  class  them 
according  to  their  merits,  and  to  distinguish  perfection  from 
deformity ;  he  alone  possesses  the  sentiment  of  the  beautiful, 
that  faculty  which  permits  him  to  admire  the  Creator  in  his 
works,  and  givqs  him  the  right  to  place  himself  in  the  first 
rank  of  animated  beings. 

The  plastic  arts  receive  their  most  elevated  inspirations 
from  the  human  form,  and  it  is  to  the  efforts  of  painters 
and  sculptors  to  reproduce  it  in  its  perfection  that  we  owe 
the  treasures  of  our  museums.  It  is  often  said  of  these 
master-pieces  that  they  are  the  ideal  of  beauty,  but  we  are  not 
to  understand  from  that  something  superior  to  nature  itself. 
The  artist  may  appreciate  the  relative  beauty  of  the  models 
which  offer  themselves  to  his  eyes,  but  in  ceasing  to  follow 
nature  and  in  endeavouring  to  become  her  superior,  he  could 
only  bring  forth  an  imaginary  product,  a  monstrosity.  Ana- 
tomy, should  be  his  first  study;  if  he  forgets  its  precepts  he 
becomes  incorrect,  like  the  musician  who  offends  against  the 
laws  of  harmony.  The  ideal  is  not  therefore  a  forin  more 
perfect,  it  is  the  perfection  of  the  natural  form  itself  which  the 
arlist  strives  to  attain,  either  by  drawing  inspiration  from  a 
single  model,  or  by  uniting  in  a  single  figure  all  the  details  which 
he  has  borrowed  from  different  individuals.  Far  from  seeking 
to  surpass  nature  he  feels  that  his  hand  is  powerless  to  render 
completely  the  impression  which  his  practised  eye  receives. 

Within  certain  limits  he  may  nevertheless  exaggerate  or 
weaken  some  detail  of  form,  and  that  too  without  ceasing  to 
imitate  nature,  who  shows  him  in  this  manner  how  he  may 
embody  the  character  and  the  physiognomy.  The  painter 
and  the  sculptor  therefore  may  rightly  allow  themselves  a 
certain  latitude  in  lines  and  proportions;  it  is  a  poetical 


Fig.  8.-— Apollo  BjlvcAere, 


Fig.  9. — The  Venus  of  Milo. 


THE    HUMAN    FORM SKIN.  19 

license,  analogous  to  that  which  allows  a  musician  to  obtain 
grand  effects  by  momentary  discords.  To  us  then  it  seems 
that  in  questions  of  this  nature  the  critic  should  proceed  with 
a  great  deal  of  reserve.  The  right  of  the  anatomist  to  point 
out  an  irregularity  cannot  be  contested,  and  the  artist  should 
be  warned  that  to  genius  alone  can  such  be  permitted ;  but 
even  if  we  admit  that  all  the  criticisms  addressed  to  painting 
or  to  sculpture  in  the  name  of  the  natural  sciences  are  well 
founded,  who  could,  in  the  presence  of  a  master-piece, 
obstinately  dwell  upon  a  fault  of  detail? 

As  regards  the  inspiration  drawn  from  the  human  form,  the 
beauty  of  Raphael's  Madonnas  and  the  admirable  paintings, 
of  the  Venetians  impress  us  perhaps  still  more  than  statuary. 
Under  the  pencil  of  the  great  masters  it  is  man  himself  that 
we  see.  What  is  more  beautiful  than  the  "Vierge  a  la 
Chaise,"  or  than  that  "Violante"  painted  by  Giorgione,  of 
which  Venice  formerly  possessed  the  glowing  figure? 

In  sculpture  the  form  alone  is  seen,  painting  adds  the 
illusion  of  colour  and  the  transparency  of  tone;  the  figures 
of  the  statuary  have  exactness  in  movement  and  flexibility 
of  form,  the  painter  vitalizes  his  creations,  gives  light  and  life 
to  the  eye,  and  makes  the  blood  circulate  through  the  skin, 
which  he  seems  to  steal  from  the  living  model. 

The  skin  is  a  membraneous  tissue,  resistant  and  flexible, 
varying  in  density  and  thickness  according  to  locality,  which 
covers  the  whole  body  and  completes  the  form  by  softening 
the  contours.  It  adheres  to,  and  is  intimately  united  with, 
the  subcutaneous  cellular  tissue  by  fibrous  prolongations. 
At  some  points  it  receives  aponeurotic  insertions,  as  in  the 
palm  of  the  hand  and  the  sole  of  the  foot;  at  others,  as  on 
the  neck,  for  instance,  the  muscular  fibres  are  attached  to 
the  skin,  and  mingle  with  the  fibres  of  its  deeper  layer. 
There  are  folds  in  the  skin,  sometimes  temporary  and  ai 
others  constant,  which  result  from  the  flexion  of  the  parts  or 
from  the  contraction  of  the  muscles,  becoming  more  marked 
with  age,  and  more  or  less  numerous  and  profound  as  the 
subject  is  inclined  to  leanness  or  to  obesity. 

The   skin   slides  over  the   organs  within  certain  variable 


26  THE    HUMAN    BODY. 

limits,  according  as  the  cellular  tissue  which  it  carries  with 
it  is  more  or  less  relaxed,  and  as  it  is  itself  thick  or  thin. 
Thus  it  is  movable  on  the  back  of  the  hand  and  top  of 
the  foot,  on  the  front  of  the  neck  and  on  the  surface  of  the 
joints;  it  is  almost  immovable  on  the  cranium,  on  the  palm 
of  the  hand,  and  on  the  sole  of  the  foot. 

Elastic,  very  extensible,  and  very  resistant,  it  sustains, 
without  being  torn,  violent  shocks  and  great  compression;  as 
in  certain  wounds  by  firearms,  for  instance,  the  projectile 
will  penetrate  the  clothing  to  the  skin,  and  injure  the  organs 
which  it  covers  without  itself  being  broken. 

The  skin  is  the  organ  of  feeling,  its  surface  is  endowed 
with  a  sensibility  which  becomes  extremely  delicate  at  several 
points.  Being  constantly  in  more  or  less  intimate  contact 
with  the  atmosphere,  it  transmits  to  the  economy  the  influ- 
ence of  external  agents ;  and  it  is  partly  by  its  tissues  that  the 
fluids  and  gases  are  eliminated,  which  have  done  their  office, 
and  are  to  be  thrown  off  as  the  ultimate  and  abandoned 
products  of  nutrition. 

This  function  of  continual  exhalation  makes  the  skin  the 
regulator  of  the  temperature  of  the  body.  When  the  tern-, 
perature  of  the  organism  is  elevated  either  by  motion  or  any 
other  internal  or  external  cause,  the  sweat  immediately 
appears,  and  the  cooling  or  loss  of  heat  caused  by  its  evapo- 
ration reduces  the  temperature  to  its  normal  standard. 
Lavoisier  was  the  first  who  clearly  explained  this  function, 
so  important  from  its  utility,  and  from  the  serious  conse- 
quences which  result  from  its  disturbance. 

Almost  entirely  deprived  of  the  covering  which  nature  has 
given  to  animals,  the  colour  of  the  human  skin  exhibits  the 
richest  and  greatest  variety  of  shades.  This  colour  is  inces- 
santly modified  by  the  sensations,  the  movements,  by  moral 
or  physical  emotions;  and  the  transparency  of  its  tissues 
give  as  much  delicacy  as  vigour  to  the  tones  which  animate 
it;  it  is  not,  as  in  the  plumage  of  birds  or  in  the  shells  of 
molluscs,  an  assemblage  of  brilliant  colours,  often  without 
transition,  but  it  is  a  blending  at  once  the  most  harmonious 
and  the  most  striking;  it  is  light  in  its  softest  changes,  w 
its  most  dazzling  splendour. 


THE    SKIN — -EPIDERMIS. 


21 


On  examining  the  thickness  of  the  skin,  we  first  find  on 
the  surface  a  thin  transparent  membrane,  a  sort  of  organic 
varnish,  designed  to  receive  the  contact  of  the  air  and  of 
external  objects.  This  is  the  epidermis.  Elastic  and  very 


Fig.  io.— The  Skin. 

A.  Section  of  skin  under  the  microscope. 

a  b.     Superficial  and  deep  layers  of  epidermis. 

c.  Dermis — true  skin. 

(/.   Fatty  areas  of  the  deeper  portions  of  the  dermis. 

d.  Muscular  layer  subjacent  to  t)ie  skin. 
t  e' .    Sweat  glands  and  ducts. 

f.     Hair-follicle  and  sebaceous  gland. 

B.  Hair  seen  under  the  microscope. 

flexible,  it  lends  itself  to  every  movement  of  the  skin,  pro- 
tecting its  exquisite  sensibility  and  modifying  its  property  of 
rapidly  absorbing  gases  and  soluble  bodies.  Although  this 
membrane  is  so  thin,  we  can  discover  a  superficial  or 
horny  layer  and  two  deeper  layers.  The  first,  the  true 
epidermis,  thickens  and  becomes  callous  under  the  influence 
of  rubbing  or  pressure,  as  for  instance  on .  the  heel.  The 
other  two  layers  are  the  mucous  network  of  Malpighi  and  the 
pigmentary  layer.  It  is  in  the  substance  of  this  last  especially 
that  the//£w/z/,  the  colouring  matter  of  the  skin,  is  developed. 


22  THE    HUMAN    BODY. 

It  is  a  black  or  brownish  substance,  more  or  less  abundant 
according  to  the  region  of  the  body,  individual,  or  race,  but 
constantly  existing  in  normal  conditions,  alike  in  Europeans 
and  in  the  people  of  Soudan  and  Australia.  The  presence 
of  this  pigment  and  its  unequal  distribution  contribute  to 
the  variety  of  complexion  exhibited  in  the  white  race. 

Under  the  pigmentary  layer  is  the  dermis,  the  thickest  and 
most  resistant  part  of  the  skin ;  it  is  white,  semi-transparent, 
and  is  composed  of  fibres  of  cellular  tissue,  fasciculated  and 
very  dense;  of  elastic  fibres,  ramified  and  disposed  in  net- 
work ;  and  of  contractile  fibre  cells. 

Immediately  under  the  epidermis  the  surface  of  the  dermis 
is  covered  with  papilla,  little  conical  or  rounded  elevations 
formed  by  the  extremities  of  the  nerves  and  vessels,  which 
are  divided  into  nervous  papillae  and  vascular  papillae.  Each 
nervous  papilla  is  surmounted  by  an  organ,  which  from  its 
function  and  its  microscopic  dimensions  is  called  a  tactile 
corpuscle  or  corpuscle  of  touch.  They  are  much  less  numerous 
than  the  other  papillae,  and  are  not  found  everywhere  on  the 
skin.  They  are  seen  on  the  palm  of  the  hand  and  on  the 
lateral  and  palmar  surfaces  of  the  fingers,  on  the  sole  of  the 
foot,  on  the  tongue,  the  lips,  and  some  other  points.  The 
epidermis  follows  exactly  the  shape  of  these  papillae,  and 
thus  forms,  in  tracing  the  furrows  which  separate  them,  those 
graceful  meandering  lines  and  elegant  curves  which  we  see 
especially  on  the  palm  of  the  hand.  Very  dense  at  its  thickest 
portion,  the  structure  of  the  dermis  grows  more  relaxed  on 
approaching  its  lower  face,  and  forms  spaces  or  areolae  in 
which  adipose  tissue  is  developed,  and  at  last  it  intimately 
unites  itself  to  the  subcutaneous  cellular  tissue,  from  which 
the  dermis  receives,  and  to  which  it  sends,  fibrous  prolonga- 
tions. 

Gratiolet  is  inclined  to  admit  that  these  so-called  nervous 
papillae  are  almost  entirely  wanting  in  nerves.  He  compares 
them  to  little  keys,  so  to  speak,  pressing  lightly  on  a  very 
sensitive  surface;  and  leaving  there  only  very  limited  impres- 
sions. 

Other  connections  also  exist  between  the  tegument  and 
the  subcutaneous  cellular  tissue:  these  are  the  nerves  and 


SWEAT-FOLLICLES — SEBACEOUS   GLANDS.  23 

the  lymphatics  and  blood-vessels,  which  arise  from  the 
skin  or  terminate  in  it ;  and  the  follicles  or  glands,  which  are 
situated  in  the  substance  of  the  dermis,  according  to  most 
authors,  but  in  the  subcutaneous  adipose  tissue,  according  to 
Robin.  These  send  the  product  of  their  secretions  by 
special  ducts  to  the  epidermis.  These  ducts  traverse  the 
substance  of  the  skin  sometimes  in  straight  and  sometimes 
in  twisted  lines,  and  give  passage,  some  to  hairs,  to  the 
beard  and  to  products  of  this  nature  which  are  formed  in 
the  bulb  of  the  hair-follicles ;  and  others,  to  the  secretions  of 
the  swsat-follicles  and  the  sebaceous  glands.  The  orifices  of 
the  sweat-follicles,  situated  at  the  base  of  the  papillae,  exhale 
the  secretion  in  the  form  of  insensible  perspiration,  or  in 
the  form  of  little  drops  on  the  surface  of  the  skin.  Those 
of  the  sebaceous  glands  open,  some  into  the  hair-ducts,  and 
others  on  the  surface  of  the  epidermis,  and  furnish  to  that 
membrane  and  its  dependencies  a  fatty  substance  which 
seems  to  be  designed  to  preserve  the  softness  of  the  skin, 
and  to  protect  it  from  injury  or  change  from  the  sweat;  we 
find  them  therefore  in  the  greatest  abundance  at  those 
points  where  the  transpiration  is  most  active. 

Of  these  glands  and  follicles  of  which  the  microscope 
shows  us  the  details,  some  attain  the  size  of  a  grain  of  millet, 
but  most  of  them  hardly  reach  a  millimetre  in  diameter. 
Their  orifices  are  on  the  surface  of  the  epidermis,  a  point 
long  disputed,  but  now  admitted  by  anatomists.  But  these 
orifices  are  not  what  were  formerly  denominated  pores.  It 
was  supposed  that  there  were  gaps  or  spaces  in  the  skin 
analogous  to  those  in  a  sieve,  and  that  the  cutaneous  secre- 
tions issued  from  these  gaps;  but  neither  in  the  epidermis 
nor  in  the  skin  are  there  any  such  gaps,  and  it  will  be  seen 
from  the  preceding  description  wherein  the  doctrines  of  the 
ancients  differ  from,  and  wherein  they  resemble,  those  of  our 
own  day. 

The  epidermis  is  regarded  by  anatomists  as  impermeable, 
and  yet  experiment  proves  that  even  the  perfect  skin  allows 
gases  and  fluids  to  penetrate  the  organism.  If  we  do  not 
admit  that  this  absorption  takes  place  through  orifices  at 
the  surface  of  the  epidermis,  and  if  we  suppose  it  to  take 


24  THE   HUMAN    BODY. 

place  by  imbibition  or  endosmosis,  it  is  plain  that  the  skin 
is  permeable,  at  least  under  certain  conditions.  But  it  is 
not  equally  so  throughout  its  whole  extent;  the  thicker  the 
epidermis  the  slower  and  more  difficult  is  the  absorption ;  in 
short,  the  skin,  like  all  the  other  tissues,  absorbs  certain  sub- 
stances to  the  exclusion  of  others. 

We  shall  have  occasion  to  discuss  these  phenomena  in 
treating  of  absorption. 

After  enveloping  the  body,  the  skin  folds  back  upon  the 
openings  which  give  access  to  its  cavities,  and  modifying  its 
nature,  becomes,  under  the  name  of  the  mucous  membrane, 
an  internal  skin,  analogous,  as  we  shall  see  further  on,  to 
the  external  skin  in  its  structure,  its  functions,  and  in  the 
intimate  connection  which  is  established  by  their  reciprocal 
influence  and  unity. 


CHAPTER  III. 


Structure  of  the  body. — Bones,  cartilages,  joints — Muscles,   tendons, 
aponeuroses. 

Bones. — The  bones  are  the  framework  of  the  human 
body.  They  are  formed  of  a  hard  and  extremely  resistant 
tissue,  and  they  surround  more  or  less  completely  with 
solid  walls  the  cavities  containing  delicate  organs;  they 
provide  attachments  and  support  for  the  soft  parts,  and 
furnish  a  fulcrum  for  the  movements  of  the  body;  and  lastly, 
by  their  resistance  they  permanently  maintain  the  propor- 
tions between  its  different  parts. 

The  osseous  substance  is  composed  of  calcareous  salts — 
phosphate  or  carbonate  of  lime — intimately  combined  with 
organic  principles,  the  decomposition  of  which  produces 
gelatine. 

If  the  bone  is  immersed  for  a  length  of  time  in  hydro- 
chloric acid,  the  calcareous  matter  will  be  dissolved,  and  the 
isolated  gelatine  will  retain  perfectly  the  form  of  the  bone; 
and  in  the  same  manner  if  the  gelatine  be  destroyed  by 
combustion,  the  lime  which  remains  will  show  the  normal 
form  and  dimensions  of  the  bone.  In  a  gelatinous  state  the 
bone  is  soft  and  flexible;  in  the  calcareous  state  it  is  hard, 
rigid,  and  brittle ;  in  a  normal  condition  each  of  these  con- 
stituent substances  serves  as  a  corrective  to  the  other;  and 
their  properties  united  give  to  bone  its  solidity  and  its 
elastic  resistance. 

In  the  osseous  tissues,  as  in  all  those  of  the  body,  we  re- 
cognize a  movement  of  composition  and  of  decomposition,  of 
molecules  assimilated  and  again  rejected  after  a  certain  time; 
but  in  none  of  the  organs  so  well  as  in  the  bones  has  it 


26  THE    HUMAN    BODY. 

been  possible  to  demonstrate  this  double  movement  of  nutri- 
tion. If  we  mingle  madder  with  the  food  of  an  animal,  the 
bones  soon  become  red,  and  they  regain  their  original  colour 
when  the  colouring  matter  ceases  to  form  part  of  the  food. 
Or,  more  conclusive  still,  if  the  madder  be  given  for  a  while 
and  then  omitted,  and  after  a  time  be  again  given,  the  bones 
show  a  white  layer  between  two  red  ones,  which  proves  that 
they  grow  from  the  circumference  toward  the  centre,  by  the 
ossification  of  the  deepest  layers  of  the  periosteum. 

The  bones  are  divided  according  to  their  form  into  long, 
flat,  and  short  bones.  The  long  bones,  which  are  first  and 
most  rapidly  developed,  are  more  dense  in  the  middle  or 
body  of  the  bone  than  at  their  extremities.  This  body  is 
formed  principally  of  a  compact  bark  or  rind  of  ivory-like 
tissue,  and  is  pierced  throughout  its  length  by  the  medullary 
canal;  the  extremities  are  composed  of  spongy  tissue  en- 
veloped by  a  thin  layer  of  ivory  tissue.  The  long  bones 
combine  to  form  the  limbs  and  the  thorax;  designed  to 
serve  as  levers  or  columns,  they  are  twisted  on  their  axes  or 
bent  so  as  to  offer  the  greatest  possible  resistance  in  exert- 
ing a  force  or  supporting  a  weight. 

The  flat  bones  form  the  walls  of  the  cavities  of  the 
cranium,  of  the  chest,  and  of  the  pelvis;  they  are  thinner  in 
the  middle  than  at  the  edges,  and  are  composed  of  two 
leaves  or  tables  of  ivory  tissue  resting  upon  and  confounded 
with  each  other  at  some  points,  and  separated  at  others  by 
a  layer  of  spongy  tissue. 

The  short  bones  are  very  irregular  in  form  and  difficult  to 
describe;  very  spongy  in  texture  and  relatively  light.  They 
develop  later  and  more  slowly  than  the  others,  and  they  are 
placed  in  groups  in  parts  of -the  body  where  the  bony  frame 
must  possess  a  limited  power  of  motion,-  and  yet  be  very 
firm,  as  in  the  foot,  in  the  hand,  and  in  the  spinal  column. 

There  are  198  bones  in  the  human  skeleton  when  it  has 
reached  its  perfect  development.  On  the  surface  of  the 
bones,  and  especially  at  the  extremities  of  the  long  ones, 
there  are  prolongations  of  different  forms,  designed  either  to 
join  the  bones  together,  or  to  serve  for  the  attachment  and 
insertion  of  muscles  or  ligaments.  These  prolongations  are 


Fig.  it.— Skeleton. 


EPIPHYSIS — PERIOSTEUM — CARTILAGE.  29 

the  apophyses,  which  are  distinguished  by  anatomists  by 
names  suggested  by  their  position,  by  their  use,  or  borrowed 
from  objects  of  which  they  recall  more  or  less  exactly  the 
form. 

The  body  of  the  long  bones  and  the  central  part  of  the 
large  bones  are  developed %  before  the  extremities  and  the 
edges.  The  extremities  of  the  long  bones  are  cartilaginous 
in  early  life,  their  articulating  surfaces  are  formed  of  cartilage 
adherent  to,  but  not  continuous  with,  the  bone  to  which  it 
belongs.  This  is  the  epiphysis,  which  afterward  becomes 
ossified,  but  is  not  perfectly  united  to  the  bone  till  about  the 
age  of  twenty.  Some  of  the  large  bones  also  present  epiphyses 
on  their  edges  or  borders. 

A  white  fibrous  membrane,  resistant  in  youth  and  reduced 
to  a  thin  layer  of  cellular  tissue  in  the  adult  and  aged,  which 
is  called  the  periosteum,  envelops  every  part  of  the  bones, 
except  where  they  are  covered  with  cartilage  and  where  the 
tendons  and  ligaments  are  attached.  The  periosteum  adheres 
closely  to  the  bone,  and  distributes  a  network  of  vessels  through 
its  substance.  Recent  surgical  investigations  have  shown 
that  the  periosteum  plays  an  important  part  in  the  partial 
reproduction  of  the  bone  after  certain  operations. 

Cartilage. — To  the  bony  system  belong  the  cartilages, 
which  are  formed  of  what  might  be  termed  tissue  in  a  state 
of  transition  between  fibrous  and  bony  substance.  This 
tissue,  homogeneous  in  true  cartilage,  mingled  with  fibrous 
substance  in  the  fibre-cartilaginous  parts,  is  elastic  and  flexible, 
and  in  colour  either  yellowish  or  pearl-white.  The  cartilages 
unite  the  bones  at  those  points  where,  as  in  the  chest,  the 
bony  frame  must  yield  to  expansive  movements;  they  furnish 
a  flexible  skeleton  to  certain  organs,  as  the  external  ear,  for 
example,  the  nose,  the  eyelids,  and  the  larynx;  and  lastly,  they 
play  an  important  part  in  the  joints. 

No  part  of  the  organism  shows  more  clearly  than  the  bony 
system  the  care  which  nature  has  taken  to  provide  during 
infancy  the  gifts  of  which  she  is  so  prodigal  in  maturity,  and 
which  she  withdraws  little  by  little  in  old  age.  During  in- 
fancy, when  protected  by  maternal  care  and  when  the  growth 
should  be  rapid,  the  gelatine  predominates  in  the  bones; 


30  THE    HUMAN    BODY. 

they  are  flexible  and  have  only  a  resistant  power  propor- 
tionate to  the  movements  and  efforts  of  infancy;  it  is  the 
branch  full  of  sap,  but  of  which  the  woody  portion  is  not 
yet  developed.  In  youth,  as  the  muscular  power  augments, 
the  bones  gradually  become  more  solid;  the  extremities,  at 
first  cartilaginous,  become  ossified;  the  epiphyses  unite  with 
the  body  of  the  bone;  and  the  articulating  cartilages  gain 
more  consistence.  In  the  adult  at  last  the  bones  are 
complete.  They  are  able  to  resist  the  muscular  efforts  of 
maturity,  and  perform  their  functions  perfectly,  like  all  other 
parts  of  the  organism  which  are  fully  developed.  But  age 
approaches,  the  strength  decreases,  nutrition  falls  off,  the 
bones  become  more  solid,  their  power  of  resistance  lessens, 
the  medullary  canal  enlarges,  the  proportion  of  calcareous 
salts  in  the  osseous  substance  augments,  the  bones  are  harder 
but  they  are  also  more  brittle.  Thus,  as  each  phenomenon 
of  life  is  linked  with  every  other,  we  find  the  bones  of  a 
child  quickly  and  easily  restored  if  broken;  in  the  adult  the 
process  may  be  longer,  but  is  generally  easy  and  complete; 
in  the  old  man  the  reunion  of  the  fragments  takes  place 
slowly,  and  sometimes  cannot  be  effected  at  all.  The  deli- 
cate twig,  which  afterwards  became  a  vigorous  branch,  is 
now  dry  and  destined  to  speedy  decomposition. 

Joints. — The  bones  are  attached  to  each  other,  either  by 
their  extremities  or  their  sides,  in  such  a  manner  as  to  per- 
mit freedom  of  motion  to  a  greater  or  less  extent  between 
the  different  parts  of  the  skeleton  and  of  the  body.  Held 
together  by  a  sort  of  cog-wheel  system,  by  the  fitting  of  a 
projection  into  an  appropriate  cavity,  or  by  juxtaposition, 
they  are  maintained  in  connection  either  by  the  reciprocal 
attachments  of  these  projections,  or  by  envelopes — the 
articular  capsules — and  by  ligaments,  constant  in  their  nature, 
but  varying  in  form  and  disposition,  according  to  the  dif- 
ferent movements  which  they  are  designed  to  permit  and 
insure. 

This  assemblage,  this  connection  of  the  bones,  is  termed 
a  joint.  Joints  are  classed  according  to  the  form  of  the 
articulating  surfaces,  and  according  to  the  extent  and  variety 
of  the  movements  produced  by  them.  The  bones  of  the 


SUTURES — VARIETY    OF    FORM    IN    JOINTS.  31 

skull  are  attached  by  the  notches  on  their  edges;  these  are 
termed  the  sutures  of  the  skull.  They  ossify  with  age,  and 
may  be  considered  temporary  joints,  or  rather  a  transition 
between  the  separation  of  the  bones  and  their  unification. 
The  other  joints,  on  the  contrary,  are  permanent,  and  de- 
signed to  leave  to  the  bones  which  they  unite  a  mobility 
which  continues  during  life. 

In  some  of  the  joints  the  surfaces  are  nearly  plane  or  flat; 
others  present  projections  with  corresponding  depressions; 
sometimes  there  is  a  segment  of  a  spheroid  upon  which  the 
cavity  which  receives  it  moulds  itself;  sometimes  a  cylinder 
which  turns  upon  its  axis  in  a  ring,  or  a  pulley-groove  around 
which  slides  an  apophysis,  or  a  mortise  in  which  a  tenon 
is  set. 

Here,  as  in  all  the  works  of  nature,  we  admire  the  inex- 
haustible variety  of  form  and  of  mechanism.  Doubtless  there 
exists  between  certain  articulations  resemblances  which  per- 
mit them  to  be  classed  together;  but  all  are  as  distinct  as 
the  bones  which  they  unite,  and  like  them  present  diversity 
of  character.  Separately  considered  they  astonish  us  no 
less  by  the  multiplicity  of  detail  in  their  mechanism,  whether 
we  examine  the  most  complex  or  those  whose  surfaces  pre- 
sent the  least  irregularity.  In  fact  we  nowhere  mid  a  uniform 
plan,  and  the  projections  as  well  as  the  depressions  are 
curved  in  the  most  capricious  manner. 

These  details  of  the  general  outline  belong  to  no  precise 
geometrical  form ;  they  are  neither  cubes  nor  spheres,  neither 
cylinders,  cones,  nor  pyramids,  although  in  anatomical 
language  these  terms  are  applied  to  them.  There  is  an  assem- 
blage in  the  same  apophysis,  or  in  the  same  cavity,  of  curved 
surfaces  borrowed  from  the  most  widely  differing  solids, 
united  under  angles  the  most  varied,  and  modelled  on  sinu- 
osities which  defy  geometrical  description. 

In  addition  to  these  distinctive  characters  of  the  joints, 
we  may  mention  others  which  are  common  to  them  all.  All 
the  joints  have  cartilages  covering  the  bones  which  form 
them;  all  are  kept  together  by  special  ligaments,  and  are 
lined  with  a  sy  no  vial  membrane,  whose  functions  we  shall 
subsequently  describe. 


32  THE    HUMAN    BODY. 

The  polish  on  the  articular  cartilages  facilitates  their  sliding 
over  each  other,  and  lessens  the  friction  of  the  bony  ex- 
tremities, while  their  elasticity  diminishes  the  pressure  and 
deadens  the  shocks  to  which  the  joints  are  subject.  The 
thickness  of  these  cartilages  is  proportioned  to  the  motion 
and  the  pressure  which  they  are  designed  to  support,  and  it 
is  greatest  at  the  centre  of  the  convexity  of  protuberances 
and  on  the  borders  of  cavities.  The  articular  cartilages 
never  ossify,  differing  in  this  respect  from  those  which,  as  in 
the  thorax  for  example,  maintain  continuity  and  play  the 
part  of  flexible  bones.  These  last  are  ossifying  cartilages. 
The  others  differing  in  structure,  being  without  vessels,  have 
been  compared  to  the  enamel  on  the  teeth.  In  fact,  they 
are  composed,  like  that  enamel  and  some  other  analogous 
productions,  of  an  almost  inorganic  substance,  and  mechani- 
cal injuries  are  the  only  ones  which  they  have  to  fear. 

Wherever  in  the  organism  surfaces  move  over  each  other, 
they  are  covered  with  a  membrane  which  secretes  a  fluid, 
differing  in  quality  according  as  there  is  a  sliding  or  rubbing 
of  the  organs.  In  the  interior  of  the  joints  the  membranes 
are  termed  synovial  membranes,  and  secrete  a  fluid  called 
synovia,  because  its  physical  characters  resemble  those  of 
the  white  of  an  egg.  The  synovia  is  to  the  joints  what  oil 
is  to  the  wheels  of  a  machine;  incessantly  poured  out  upon 
the  surfaces,  it  lubricates  them,  and  renders  the  movement, 
already  so  easy  owing  to  the  polish  of  the  cartilages,  still 
more  so;  it  increases  the  suppleness  and  elasticity  of  these 
last,  which  if  they  were  not  supplied  with  this  oily  fluid 
would  soon  be  worn  out,  and  motion  would  be  impossible. 
This  sometimes  results  from  certain  diseases,  and  sometimes 
also  in  old  age. 

We  have  said  that  the  joints  are  united  by  ligaments. 
This  term  is  applied  to  the  bands  or  membranes  com- 
posed of  fibrous  tissue,  flexible  and  inextensible.  The  liga- 
ments, which  are  in  the  form  of  bands,  are  sometimes  parallel 
and  sometimes  interlaced,  and  placed  either  between  the 
articular  surfaces  or  around  them.  In  the  latter  case  their 
internal  face  is  covered  with  intimately  adherent  synovial 
membrane.  The  ligaments  are  attached  to  the  bones  at  a 


CAPSULAR    LIGAMENTS. 


33 


greater  or  less  distance  from  the  articular  cartilage,  and  they 
adhere  so  strongly  that  it  is  easier  to  break  the  bone  or  the 
ligament  than  to  tear  it  from  the  spot  where  it  is  planted. 
The  membranous  ligaments — capsulary  ligaments  or  fibrous 
capsules — are  like  a  circular  band  of  which  the  two  openings 
are  fastened  to  the  bones  which  they  unite.  The  fibrous 
pads  or  cushions  which  run  round  the  circumference  of  cer- 
tain articular  cavities  are  also  considered  as  ligaments. 
They  increase  the  depth  of  these  cavities,  and  give  greater 


Fig.  12. —  Elbow-joint. 
A.  H-umerus.     B.    Ulna.     C.  Radius. 

solidity  to  their  borders,  upon  which  the  osseous  extremity 
received  there  exerts  considerable  pressure. 

Such  is  the  assemblage  of  apparatus  comprised  in  the 
joints.  The  most  perfect  machine  which  man  has  ever  been 
able  to  construct  bears  no  comparison  to  the  admirable 
mechanism  of  which  we  have  just  endeavoured  to  give  a 
general  idea,  in  the  precision,  delicacy,  and  variety  of  their 
organs  or  of  their  movements.  Even  in  their  most  com- 
plicated parts,  machines  invented  by  man  offer  nothing  but 


34  THE   HUMAN  .BODY. 

a  simple  mathematical  precision,  impossible  to  mistake,  be- 
cause all  the  surfaces  are  conceived  and  traced  out  geometri- 
cally. In  the  joints,  on  the  contrary,  all  the  lines  and  surfaces 
.are  vague  and  uncertain;  and  when  we  examine  an  articular 
extremity,  the  inferior  extremity  of  the  humerus  for  example, 
we  shall  at  first  be  tempted  to  believe  that  the  unsymmetrical 
projections  and  depressions,  the  incomplete  grooves,  and  the 
undefmable  irregularity  of  the  whole,  belong  to  a  work 
spoiled  or  modelled  at  hazard  by  a  confused  mind;  but  on 
seeing  the  action  of  the  elbow-joint  when  laid  open  by  the 
anatomist,  we  discover  that  it  is  to  this  very  irregularity  of 
the  bony  extremities,  to  the  multiplicity  of  detail,  to  the 
absence  of  symmetry,  and  to  the  more  or  less  limited  extent 
of  their  articulating  surfaces,  that  the  variety  of  movement  is 
due,  and  we  cannot  sufficiently  admire  this  assemblage,  so 
complex,  but  yet  so  justly  calculated  to  give  to  the  move- 
ments of  the  fore-arm  the  greatest  precision,  strength,  and 
rapidity,  and  to  combine  these  movements  with  those  of  the 
arm  and  the  hand. 

And  if  we  pass  from  the  most  mobile  of  these  joints  to 
those  not  at  all  or  only  slightly  movable,  the  perfect  coapta- 
tion  of  their  surfaces,  their  powerful  methods  of  union,  the 
unity  of  movement  of  the  bones,  whether  they  take  part  in 
the  motion  or  serve  only  as  fulcrums,  all  seem  to  be  as 
simple  as  possible  in  function,  although  the  whole  as  well  as 
the  details  presents  the  most  delicate  application  of  the  laws 
of  mechanics  and  statics.  We  may  add  that  here  as  well  as 
everywhere  in  the  study  of  the  works  of  nature,  we  see  the 
organs  develop  themselves  from  the  embryonic  state  to  that 
of  perfection,  under  the  influence  and  in  the  exercise  of  their 
functions.  .  But  leaving  out  the  inimitable  results  produced 
by  life  in  natural  creations,  and  considering  them  as  inor- 
ganic bodies,  the  mechanism  of  the  joints  leaves  far  behind 
all  the  most  ingenious  productions  of  art  or  science. 

The  distance  appears  to  us  greater  still  when,  instead  of  a 
combination  of  surfaces  and  the  method  of  their  union,  we 
.study,  the  action  of  the  muscles  and  the  transformations 
which  are  incessantly  taking  place  in  the  organs  of  digestion 
and. respiration.  In  unveiling  a  part  of  these  mysteries  to 


MUSCLES. 


35 


man,  the  progress  of  science  only  increases  his  admiration. 
What  would  it  be  if  life,  that  force  of  which  he  is  conscious, 
and  which  he  shares  with  all  organized  beings,  should  cease 
to  be  to  him  an  impenetrable  secret! 

Muscles. — United  by  the  joints,  the  bones  of  the  skeleton, 
taken  as  a  whole,  approach  the  form  of  the  body.  But  in 
order  to  put  these  bones  in  motion, 
and  to  bring  these  joints  into  play, 
we  must  call  to  our  aid  an  external 
force.  By  itself,  if  we  may  be  per- 
mitted a  very  familiar  comparison, 
the  skeleton  is  a  puppet  of  which 
the  different  parts  are  put  in  motion 
by  threads.  The  threads  by  which 
the  skeleton  is  moved  are  the 
muscles.  The  name  muscles  is 
given  to  the  masses  of  red  tissue 
which  constitute  the  flesh.  We 
have  already  described  the  ele- 
ments of  the  muscular  tissue;  how 
the  primitive  microscopic  bundles, 
united  into  secondary  ones',  become 
muscular  or  fleshy  fibres  easily  dis- 
tinguished by  the  naked  eye.  These 
fibres  are  parallel  or  divergent  ac- 
cording to  the  muscle,  and  assume 
different  forms.  Sometimes  it  is 
that  of  a  ribbon  (sartorius,  sterno- 
hyoid,  &c.);  sometimes  a  broad 
web-like  tissue  of  a  texture  more  or 
less  firm,  like  the  transverse  muscles 
of  the  abdomen;  in  one  region  the 
muscle,  swollen  in  the  centre,  and 
drawn  out  like  a  thread  at  the  ends, 
resembles  a  spindle  in  form  (biceps, 
straight  muscle  of  the  thigh);  in  another  it  is  fan-shaped 
(temporal,  obturator),  or  like  a  ring  (orbicular  muscle  of 
the  lips  and  eyes) ;  or  the  fibres  converge  like  the  radii  of  a 
circle  (the  diaphragm);  or  are  disposed  in  parallel  lines  like 


Fig.  13. — Biceps  muscle  of  the 
arm. 

A.  Body  of  the  muscle. 
B.  B.  Superior  tendons. 
C.  Inferior  tendons. 


36  THE   HUMAN    BODY. 

the  feathers  of  a  pen  (extensor  muscles  of  fingers).  Lastly, 
certain  organs,  the  heart  for  example,  are  nothing  but 
muscle,  or  rather  an  assemblage  of  muscles  intimately 
united. 

The  muscles  determine  the  form  and  volume  of  the  body, 
and  especially  of  the  limbs.  The  outline  depends  upon  their 
projection,  and  changes  incessantly  as  they  are  in  action  or 
in  repose.  They  are  disposed  in  layers,  deep  or  superficial, 
and  united  in  groups  or  separated  by  sheaths  and  mem- 
branous partitions.  Their  colour  varies  from  deep  red  to 
pale  rose,  'according  to  the  region  of  the  body  they  occupy, 
age,  sex,  the  constitution  and  richness  of  the  blood.  The 
stronger  the  muscle  the  redder  it  is,  and  it  becomes  still 
brighter  under  the  influence  of  exercise. 

The  muscles  of  the  human  body  number  about  350,  and 
they  are  distinguished  by  names  suggested  by  their  form, 
their  locality,  their  functions,  or  their  attachments.  Some 
are  fixed  to  the  skin,  as  several  of  the  muscles  of  the  face ; 
others  to  muscles  in  their  vicinity,  as  in  the  face  and  tongue; 
others  still  to  the  cartilages,  but  the  largest  number  to  the 
bones  by  means  of  the  tendons  or  the  aponeuroses,  of  which 
we  proceed  to  speak. 

Tendons,  aponeuroses. — In  most  of  the  muscles  we  can  dis- 
tinguish a  fleshy  portion,  which  is  essentially  the  muscle,  and 
a  fibrous  portion,  which  is  called  either  tendon  or  aponeurosis 
according  to  its  form.  The  tendons  are  fibrous  cords  of 
variable  length,  rounded  or  flattened,  of  a  pearl-white  colour, 
attached  to  the  bones  by  one  of  their  extremities  and  united 
to  muscular  fibres  by  the  other.  The  aponeuroses  are 
nothing  but  large  thin  tendons,  a  kind  of  fibrous  web  or  band 
which  accompanies  the  muscles,  separating  them  by  partitions 
or  enveloping  and  uniting  them  in  bundles.  The  tendinous 
fibres  are  generally  developed  in  the  substance  of  the  fleshy 
part  of  the  muscle,  or  on  the  surface,  which  they  cover  to  a 
certain  extent.  In  the  first  instance  they  are  inclosed,  as  it 
were,  by  the  muscle;  in  the  second,  they  envelop  it  like  a 
sheath.  This  reciprocity  gives  great  solidity  to  the  whole. 

The  muscles  and  tendons  are  united  together  by  the  direct 
adherence  of  the  extremities  of  their  fibres,  which  takes  place 


TENDONS,   APONEUROSES. 


37 


in  right  lines ;  or  by  the  insertion  of  the  fleshy  fibres  at  some 
point  in  the  length  of  the  tendon,  at  various  angles,  but  never 
exceeding  45  degrees.  Such  is  the 
force  of  this  adhesion  between  the 
two  tissues  that  rarely  if  ever  does 
external  violence  or  the  greatest 
effort  succeed  in  overcoming  it,  the 
tendon  or  the  muscle  breaks  before 
separating  at  their  points  of  union. 
We  have  already  pointed  out,  in 
speaking  of  the  articular  ligaments, 
the  remarkable  fact  that  the  adhe- 
sion of  two  organic  tissues  is  strong- 
er than  the  cohesion  of  either  of 
the  respective  tissues. 

The  tendons  and  the  aponeur- 
oses,  though  very  flexible,  are  en- 
tirely inextensible,  and  offer  there- 
fore great  resistance  to  force 
applied  to  their  length.  This  is 
one  of  the  conditions  necessary  for 
the  part  which  they  play  in  uniting 
the  organ  of  motion  and  the  object 
to  be  moved. 

Like  the  ossifying  cartilages,  the  tendons  may  be  considered 
as  a  transition  tissue.  They  partially  ossify  with  age  at  their 
points  of  insertion  into  the  bones,  but  they  are  never  entirely 
transformed  in  the  human  race,  as  in  some  animals,  the 
Gallinaceae  for  example,  into  a  bony  trunk.  Suppleness  and 
variety  of  movement  would  not  accord  with  this  transforma- 
tion; and  among  the  differential  marks  which  Plato  might 
have  added  to  his  famous  definition  of  man,  this  would  have 
sufficed  to  prevent  Diogenes  from  saying,  as  he  exhibited  the 
cock  stripped  of  its  feathers,  "Behold  Plato's  man!" 

A  relatively  slender  tendon  suffices  to  transmit  a  motive 
force  developed  by  a  certain  amount  of  contractile  fibre,  and 
the  fleshy  portion  of  the  muscles  far  surpasses  in  volume  the 
tendons  and  the  aponeuroses.  If  the  muscular  fibres  attached 
themselves  directly  to  the  bones  the  surface  of  the  bones 


Fig.  14.  — Lower  portion 
of  the  leg. 

A.  Tendon  of  Achilles. 


38  THE    HUMAN    BODY. 

would  not  be  sufficient  to  supply  space  for  them ;  this  direct 
attachment  to  large  surfaces  is  confined  to  a  few  only,  the 
others  being  attached  by  their  aponeuroses  or  tendons  to 
limited  spaces. 

The  muscles  are  at  the  same  time  contractile  and  exten- 
sible. The  muscle  shortens  by  contraction  and  increases 
in  thickness  at  the  same  time  that  its' length  diminishes;  in 
.repose  it  is  soft  and  yielding  to  touch,  in  contracting  it 
becomes  hard  and  resistant.  These  successive  changes  are 
easily  demonstrated  by  applying  the  hand  to  the  course,  of 
a  superficial  muscle,  on  the  front  of  the  arm  for  example,  on 
the  biceps.  When  the  fore-arm  is  extended  it  projects  but 
slightly  and  yields  to  pressure;  it  swells,  on  the  contrary, 
becomes  resistant,  and  forms  a  marked  protuberance,  when 
contracting  in  order  to  flex  the  fore-arm. 

The  contraction  of  a  muscle  may  also  take  place  without 
its  being  shortened.  When,  for  example,  the  fore-arm  is 
extended  upon  the  arm,  if  the  extensors  oppose  the  flexion 
by  contracting,  the  biceps  and  anterior  brachial,  both  flexor- 
muscles,  may  contract  without  their  ends  approaching  each 
other. 

Glisson,  Borelli,  and  other  anatomists  have  supposed  that 
the  muscle  increases  in  volume  during  contraction;  but  further 
experiment,  confirmed  also  by  those  of  Provost  and  Dumas, 
has  demonstrated  that  it  gains  in  thickness  only  what  it  loses 
in  length,  and  that  there  is  no  change  in  the  absolute  volume. 

In  contracting,  the  muscular  fibres  become  tortuous  and 
wavy,  wrinkles  are  formed  on  the  surface,  a  sort  of  trembling 
pervades  the  whole  mass,  and  its  temperature  is  raised. 
Becquerel  and  Breschet  have  observed  this  increase  to  reach 
half  a  degree  centigrade. 

To  the  contraction  of  certain  muscles  must  correspond 
the  inertia  or  even  lengthening  of  the  antagonistic  muscles, 
as  for  instance  when  the  fore-arm  is  flexed  upon  the  arm  or 
the  leg  upon  the  thigh,  the  extensors  of  the  fore-arm  and  of 
the  leg  take  part  in  the  movement  and  lengthen  by  means 
of  their  extensibility.  In  like  manner  the  muscular  texture 
which  forms  the  walls  of  certain  organs,  as  of  the  stomach  and 
intestines,  is  expanded  by  the  fluids  and  the  aliments,  or  by 


MUSCLES,   THEIR  ACTION.  39 

the  gases  which  are  developed  in  them.  The  flute-player  of 
antiquity  kept  his  cheeks  distended  by  means  of  a  leather 
strap.  Thus  there  is  a  constant  struggle  between  the  con- 
tractility and  the  extensibility  of  the  muscles.  But  if,  during 
the  contraction  of  certain  muscles,  as  the  flexors  of  the  arm, 
the  antagonistic  muscles,  the  extensors,  are  relaxed  and  do 
not  oppose  the  movement,  they  regulate  it  nevertheless  by 
virtue  of  a  property  named  muscular  tonicity,  which  gives  to 
their  tissues  even  when  not  contracted  a  certain  power  of 
resistance.  Thus  when  a  group  of  muscles  is  paralyzed,  the 
antagonistic  muscles  cause  by  their  contraction  a  jerking 
movement  which  has  no  regularity. 

In  contracting,  the  muscles  act  like  levers  upon  the. bones, 
and  therefore  just  so  much  less  powerfully  as  they  are  placed 
obliquely  to  the  bone.  Notwithstanding  the  larger  part  of 
the  muscles  are  attached  to  the  bones  at  an  acute  angle,  and 
their  direction  is  very  oblique  in  regard  to  the  lever  they 
are  to  move.  The  result  is  a  great  loss  of  force,  but  this 
loss  is  compensated  by  an  increase  of  volume  in  the  muscles, 
that  is  in  the  number  of  fibres  of  which  they  are  composed. 

Most  of  the  muscles  are  subject  also  to  deviations  or 
reflections  around  the  joints.  Some  even  take  a  direction 
perpendicular  to  their  original  one  in  turning  round  bony 
hooks  or  in  the  grooves  of  the  pulleys.  The  apophyses,  or 
the  protuberances  to  which  they  are  attached,  permit  them 
to  move  at  a  greater  angle  and  a  more  favourable  one  than 
the  initial  angle,  and  this  angle  gradually  increases  as  the 
bone  obeys  the  force  applied  to  it;  and  lastly,  the  relative 
direction  of  the  muscle  as  regards  the  bone  varies  according 
to  the  attitude.  These  dispositions  of  the  muscles  are  always 
adapted  to  the  kind  of  movement  to  be  executed,  to  the 
extent  or  rapidity  required,  or  to  the  force  demanded;  and 
they  are  always  so  combined  as  to  produce  the  maximum  of 
useful  result.  So  in  flexing  the  fore-arm,  in  elevating  the 
arm,  the  bones  act  as  levers  of  the  third  order.  The  biceps, 
anterior  brachial,  and  deltoid  muscles  act  as  very  short 
levers  upon  the  arm,  and  their  initial  direction  is  almost 
parallel  to  the  bone,  but  it  soon  becomes  almost  perpen- 
dicular to  it.  In  this  case  extent  and  rapidity  of  movement 


40  THE   HUMAN    BODY. 

are  important,  force  is  only  a  secondary  consideration.  If 
we  wish  to  raise  the  body  on  the  toes,  motion  is  more  limited 
but  a  great  amount  of  force  is  necessary.  The  gastrocnemius 
and  soleus  muscles,  which  form  the  calf  of  the  leg,  are  inserted 
by  the  tendon  of  Achilles — the  largest  in  the  body — to  the 
posterior  extremity  of  the  calcaneum  (or  heel-bone),  and 
perpendicular  to  its  axis ;  the  posterior  tibial  muscle  and  the 
flexors  of  the  toes  pass  behind  the  internal  malleolus  under 
the  calcaneum  and  under  the  astragalus,  as  in  the  groove  of 
a  pulley,  and  are  inserted  into  the  plantar  surface  of  the 
scaphoid  and  to  the  last  phalanges  of  the  toes,  and  these 
muscles  act  upon  the  foot,  which  serves  as  a  lever  of  the 
second  order;  that  is  to  say,  under  conditions  the  most 
favourable  to  the  power  represented  by  the  muscular  con- 
traction. 


CHAPTER  IV. 


Spinal   column.  —  Thorax. — Upper  limb  ;  shoulder ;    arm,  fore-arm, 
hand. — Lower  limb;  hip,  thigh ,  leg,  foot. 

Spinal  column. — The  spinal  column  is  the  foundation  to 
which  all  the  other  parts  of  the  skeleton  are  adapted.  It  is 
composed  of  seven  cervical  vertebrae,  twelve  dorsal  and  five 
lumbar  vertebrae,  and  is  terminated  by  the  sacrum  and 
coccyx.  Throughout  its  whole  length  runs  the  vertebral 
canal,  which  holds  the  spinal  marrow,  and  communicates 
with  the  cavity  of  the  skull.  Each  vertebra  is  composed  of 
a  body,  two  articular  processes,  two  transverse  processes,  and 
a  spinous  process.  The  body,  the  anterior  portion  of  the 
vertebra,  is  cylindrical,  and  forms  a  layer  of  the  column. 
The  articular  processes,  placed  at  the  sides,  serve  to  unite  the 
vertebrae  together;  and  \hetransverseprocesses  give  attachment 
to  the  ligaments,  muscles,  and  in  the  dorsal  regions  to  the 
ribs.  The  spinous  process,  the  posterior  portion  of  the  verte- 
bra, forms  that  series  of  projections  which  has  given  to  the 
vertebral  column  the  name  of  the  spine.  The  spinous  process 
bifurcates  into  two  plates  which  complete  the  ring  or  verte- 
bral orifice  formed  by  each  vertebra,  and  the  open  space  in 
which  forms  a  segment  of  the  vertebral  canal.  Numerous 
and  powerful  ligaments  combine  to  unite  the  vertebrae.  Be- 
tween their  bodies  fibrous  disks  in  the  form  of  lentils  are 
placed,  which  adhere  intimately  to  the  articular  surfaces ; 
they  are  formed  of  concentric  layers,  and  near  the  centre 
there  is  a  spongy  substance  saturated  with  a  fluid  analogous 
to  the  synovia.  These  disks  or  intervertebral  ligaments, 
besides  binding  together  the  bodies  of  the  vertebrae,  serve 


42  THE    HUMAN    BODY. 

to  diminish  the  shocks  and  the  pressure  to  which  they  are 
subjected  from  the  weight  of  the  parts  of  the  trunk  above 
them.  They  sink  down  and  become  thinner  while  the  body 
is  erect,  so  that  there  is  a  difference  in  the  height  between 
morning  and  evening  of  about  "02  or  '03  of  a  millimetre; 
but  repose  in  bed  restores  to  the  fibrous  disks  their  primi- 
tive thickness. 

Between  the  vertebral  plates  stretch  the  yellow  ligaments, 
remarkable  for  being  formed  of  an  elastic  tissue  which  yields 
to  the  movements  of  the  spinal  column.  Other  inextensible 
ligaments  envelop  the  spine  at  every  point,  and  give  great 
solidity  to  the  whole.  The  spinal  column  has  three  curves — 
two  backward  in  the  cervical  and  lumbar  regions,  and  one 
forward  in  the  dorsal  region.  The  ligaments  which  unite  its 
layers  permit  only  a  slight  degree  of  flexibility  in  the  upper 
dorsal  region,  but  this  is  a  little  more  extended  at  the  neck 
and  loins,  and  powerful  muscles  give  it  at  need  great  rigidity. 
And  lastly,  to  its  curves,  and  to  the  complicated  mechanism 
of  its  articulations,  it  owes  its  great  power  of  vertical  re- 
sistance. 

The  head  is  balanced  upon  the  first  cervical  vertebra, 
which  is  called  the  atlas;  the  manner  of  its  articulation  with 
the  spinal  column  permits  great  extent  and  freedom  of  move- 
ment, while  powerful  ligaments  and  muscles  give  it  great 
strength. 

Thorax. — The  ribs  are  attached  by  the  transverse  pro- 
cesses to  the  dorsal  vertebrae,  and  in  front  by  cartilages  to 
the  sternum  or  breast-bone.  They  are  twelve  in  number  on 
each  side.  The  interstices  of  this  bony  cage  are  filled  with 
muscles ;  they  cover  and  form  with  it  the  walls  of  the  chest, 
called  also  the  thorax  or  thoracic  cavity,  which  contains  the 
lungs  and  heart.  The  flexibility  of  the  costal  cartilages,  and 
the  mobility  of  the  articulations  of  the  ribs  with  the  spinal 
column,  allow  the  thorax  to  expand  and  to  -contract  in  re- 
spiration. 

Upper  limb. — Near  the  apex  of  the  cone  formed  by  the 
chest  the  upper  or  thoracic  limbs  are  attached.  They  are 
composed  of  four  parts — the  shoulder,  arm,  fore-arm,  and 
hand.  The  two  bones  of  the  shoulder  are  the  scapula^  which 


SHOULDER-JOINT,    ELBOW-JOINT.  43 

is  attached  by  muscles  to  the  upper  part  of  the  back,  and 
the  clavicle  or  collar-bone,  which  extends  from  the  sternum 
to  the  scapula,  embracing  the  top  of  the  chest.  At  the 
angle  formed  by  the  superior  border  and  the  external  edge 
of  the  scapula  an  articular  surface,  called  the  glenoid  cavity, 
receives  the  upper  extremity  or  head  of  the  humerus,  the 
bone  of  the  arm,  which  articulates  at  the  elbow  with  the 
ulna  and  the  radius,  the  two  bones  of  the  fore-arm;  these 
form  with  the  carpus  the  wrist-joint,  which  unites  the  fore- 
arm to  the  hand.  The  deltoid,  the  great  dorsal  and  great 
pectoral,  and  other  less  powerful  muscles,  combine  to  form 
the  shoulder,  and  give  motion  to  the  humerus.  The  triceps 
and  biceps  of  the  arm,  &c.,  which  surround  the  humerus, 
flex  or  extend  the  fore-arm  and  turn  it  on  its  axis;  and 
numerous  muscles  cover  the  fore-arm  and  move  the  hand. 

The  articulation  of  the  humerus  with  the  scapula  or  the 
shoulder-joint  is,  of  all  joints,  the  one  that  permits  the  most 
extended  movement.  The  shallowness  of  the  glenoid  cavity 
permits  great  freedom  of  motion  to  the  rounded  head  of  the 
humerus.  Thus  the  arm,  which  hangs  parallel  with  the  body 
in  a  state  of  repose,  can  be  raised  vertically  to  the  head, 
laterally  forward  so  as  almost  to  enfold  the  chest,  and  also 
backward,  though  in  a  more  limited  degree;  it  can  be  turned 
on  its  axis  in  all  these  positions,  and  in  the  movement  of 
circumduction  it  describes  a  very  flat  cone,  the  base  of 
which,  especially  in  front,  approaches  the  apex. 

The  elbow-joint  is  one  of  the  most  complicated  in  the 
whole  system.  The  lower  extremity  of  the  humerus,  and  the 
upper  extremities  of  the  ulna  and  the  radius,  are  adapted  to, 
and  interlock  with  each  other  by  a  series  of  rounded  surfaces 
and  pulley -grooves,  which  permit  the  fore-arm  to  flex  itself 
forwards  upon  the  arm;  while  a  protuberance  of  the  ulna,  the 
olecranon,  which  forms  the  projecting  part  of  the  elbow,  limits 
the  backward  movement  by  resting  in  a  cavity  of  the  humerus. 
It  is  into  the  olecranon  that  the  tendon  of  the  triceps  of  the 
arm,  the  principal  extensor  of  the  fore-arm,  is  inserted,  and 
we  shall  see  the  analogy  farther  on  between  this  process  and 
the  knee-pan. 

The  movements  of  the  fore-arm  singularly  multiply  by 


44  THE   HUMAN    BODY. 

their  application  those  of  the  arm.  The  radius  and  ulna 
may  be  placed  in  contact  with  the  humerus  by  flexion,  and 
again  the  radius  turns  on  its  own  axis,  without  either  the 
ulna  or  the  humerus  taking  part  in  this  movement,  which  is 
called  pronation  or  supination,  according  as  the  palm  of  the 
hand  is  turned  outward  or  inward. 

But  what  renders  the  thoracic  limb  a  perfect  organ,  that 
which  explains  the  variety  and  extent  of  its  movements,  and 
which  gives  them  all  their  value,  is  the  hand ;  that  admirable 
instrument  which  in  its  perfection  belongs  only  to  the  human 
race. 

The  hand  is  elegant  and  beautiful  in  form.  Its  isolation, 
its  contour — defined  without  stiffness — the  delicacy  of  its 
mould,  the  mobility  of  its  different  parts,  and  the  variety  in 
their  tints,  make  of  it  a  being  by  itself  in  the  human  body, 
and  give  it  an  expression  and  a  physiognomy.  Completely 
developed  even  in  infancy,  it  presents  a  most  attractive 
model  and  an  inexhaustible  subject  of  study  to  the  artist. 
Its  structure  has  led  many  philosophers  to  think  that  it  is  to 
it  alone  that  man  owes  his  superiority  to  the  animals,  and  to 
attribute  to  it  the  greatest  influence  over  the  intellectual 
faculties.  But  the  study  of  man  shows  that  we  must  reverse 
this  proposition.  The  hand  is  only  the  instrument  of  the 
intellect,  the  perfection  of  the  one  is  necessarily  dependent 
upon  that  of  the  other,  and  the  hand  of  man,  like  every 
other  part  of  his  being,  has  no  equal  in  the  animal  kingdom. 

As  for  seeing  in  the  greater  or  less  perfection  of  the  hand 
a  sign  of  the  degree  of  intelligence,  and  carrying  it  so  far  as 
to  distinguish  between  the  hand  of  a  man  of  talent  and 
genius,  and  that  of  a  fool  or  a  man  of  moderate  ability — this 
is  a  theory  which,  speciously  presented,  might  perhaps  be 
entertained  as  a  subject  having  curious  aspects,  but  on  no 
other  ground.  In  short,  if  the  hand  of  the  idiot  is  alike 
badly  developed  with  the  brain — if  we  believe  that  an  arrested 
development  of  the  fingers,  or  the  presence  of  supernumerary 
ones,  are  signs  of  degeneration  in  the  race — are  we  to  con- 
clude that  perfection  of  the  thoracic  limbs  is  the  rule,  as  has 
been  said,  in  men  of  eminence?  We  need  not  go  so  far 
back  as  Esop  for  an  example  of  a  great  mind  in  a  deformed 


THE   HAND — WRIST-JOINT.  45 

body.  Concte,  Luxembourg,  Pope,  and  other  illustrious  and 
celebrated  men,  were  victims  of  rickets.  They  had  long  and 
knotty  hands,  one  of  the  most  constant  signs  of  this  malady. 
If  men  of  inferior  intelligence  often  have  thick  and  inflexible 
hands,  it  is  because  they  are  often  born  under  conditions  which 
impose  rough  work  upon  them.  They  receive  as  a  heritage, 
with  the  toil  of  their  fathers,  this  clumsiness  of  form,  which  is 
the  consequence  of  this  toil.  The  hand  of  the  man  who  is 
not  forced  by  his  position  to  manual  labour  is  always  finer 
and  more  delicate  than  that  of  the  workman,  and  he  trans- 
mits to  his  children  this  detail  of  conformation  as  well  as  the 
general  resemblance.  The  delicacy  of  the  limbs,  the  prin- 
cipal element  of  their  elegance,  is  therefore  a  sign  of  race 
rather  than  of  intelligence,  and  belongs  especially  to  the 
oriental.  The  hand  of  a  European  cannot  enter  the  guard 
of  an  Indian  sword  or  poniard.  Shall  we  conclude  from 
that  that  the  Anglo-Saxon  or  the  Norman  has  less  intelligence 
than  the  Arab  or  the  Hindoo?  De  Blainville  relates  that 
Re'camier  attached  a  certain  importance  to  the  form  of  the 
hand,  and  was  accustomed  to  examine  those  of  his  pupils 
with  this  idea.  "Mine,"  he  adds,  "were,  like  the  others,  sub- 
mitted to  the  inspection  of  the  master,  and  the  result  was  not 
unfavourable  to  me."  Re'camier  being  present,  confirmed 
the  statement  of  the  former  pupil  of  the  Hotel-Dieu,  now 
become  an  eminent  naturalist.  But  the  hand  of  De  Blain- 
ville was  neither  fine  nor  elegant;  it  was  a  well-made, 
vigorous,  and  muscular  hand,  like  the  body  to  which  it 
belonged;  equally  skilful,  in  fact,  in  holding  a  sword,  a 
pencil,  or  a  scalpel. 

The  wrist-joint,  which  unites  the  hand  to  the  fore-arm, 
resembles  in  its  mechanism  that  of  the  shoulder.  Eight 
bones  of  different  and  very  complicated  forms  constitute  the 
wrist  or  carpus.  Three  of  these  form  the  articulation  with 
the  fore-arm,  the  others  are  united  to  the  five  bones  of  the 
metacarpus^  the  palm,  or  middle  part  of  the  hand,  to  which 
the  fingers  are  attached.  These  are  composed  of  two  pha- 
langes in  the  thumb,  three  in  the  index,  middle,  ring,  and 
little  fingers.  The  first  three  bones  of  the  carpus  are  grouped 
in  such  a  manner  as  to  present  an  ellipsoid  surface  on  the 


46 


THE   HUMAN    BODY. 


side  of  the  fore-arm;  a  condyle  which  is  received  by  the 
elliptic  cavity  formed  by  the  inferior  extremity  of  the  radius 
and  ulna.  The  hemispheric  head  of  the  humerus  turns  oh 
its  axis  in  the  glenoid  cavity,  but  this  movement  is  prevented 
in  the  hand  by  the  elongated  form  of  the  condyle  of  the 
carpus.  The  rotation  of  the  ulna  supplies  this  want,  and  the 
hand  turns  with  the  bones  which  are  attached  to  it  in 


Fig.  15. — The  hand,  palmar  aspect. 

A.  Short  abductor  muscle  of  tlie  thumb, 
above  and  outside  of  ivliich  is  seen 
the  opposing  muscle  (opponenspollicis]. 

B.  Slwrtjlexor  of  thujnb. 

C  C.    Tendons  of  the  superficial  flexor 

of  the  fingers. 
D.  Sheath  of  the  tendons. 
E  E.    Tendons  of  the  deep  flexor. 


Fig.  1 6. — The  hand,  dorsal  aspect. 
A.  Annular  ligament  of  the  inrist. 
B  B.  Tendons  of  the  common  extensor 

of  the  fingers. 
C  C.    Tendinous  expansions  fastening 

tlie  tendons  together. 


supination  and  pronation.  Further,  it  has  a  separate  move- 
ment in  flexing  the  hand  forward,  backward,  or  sidewise. 
In  circumduction  it  describes  a  cone,  and  makes  many 
other  movements  in  common  or  singly. 

The  numerous  muscles  which  determine  these  movements 
form  a  very  complicated  mechanism.     Their  tendons  are 


ACTIONS    OF   THE    HAND.  47 

interlaced  and  bound  together  by  bands  and  aponeurotic 
fibres,  and  from  this  results  a  more  or  less  complete  unity  of 
action.  It  is  sometimes  difficult  to  make  a  movement  with 
a  single  finger  without  the  others  taking  part  in  it,  as  in 
executing  instrumental  music,  for  instance ;  but  practice  gives 
to  these  movements  perfect  independence.  The  mechanism 
of  the  movements  of  the  hand  has  been  made  singularly  clear 
by  the  recent  experiments  of  M.  Duchenne  of  Boulogne,  who 
has  succeeded  in  distinguishing  by  means  of  electricity,  the 
action  not  only  of  different  orders  of  muscles,  but  also  of 
each  particular  one.  Gerdy  counts  thirty-four  distinct  move- 
ments of  the  hand,  and  if  we  include  the  combinations  of 
these  different  movements  we  shall  reach  a  much  higher 
number.  The  opposition  of  the  thumb  to  the  other  fingers, 
alone  or  united,  is  of  all  these  movements  that  which 
especially  characterizes  the  human  hand,  in  which  alone  it 
exists  in  its  perfection.  This  action  of  the  thumb  results 
from  its  length,  from  the  first  metacarpal  bone  not  being 
placed  on  the  same  plane  as  the  other  four,  as  is  the  case  in 
the  monkey,  and  from  the  action  of  a  muscle — the  long 
flexor  of  the  thumb — peculiar  to  the  human  hand.  This 
muscle  completes  the  action  of  the  other  motor  of  the 
thumb,  and  permits  man  to  hold  a  pen,  a  graver,  or  a  needle  ; 
it  gives  to  his  hand  the  dexterity  necessary  in  the  execution 
of  the  most  delicate  work;  it  is  the  attribute  of  his  intelli- 
gence. In  repose  the  hand  of  man  is  presented  in  an 
attitude  half  opposed  to  the  thumb;  but  it  is  not  so  in  the 
monkey,  even  in  the  species  most  resembling  man.  It  is 
opposable  in  these  animals,  but  much  less  so  than  in  man; 
and  the  five  bones  of  the  metacarpus  being  on  the  same 
plane,  the  fingers — or  toes — can  be  placed  flat  upon  the 
ground  in  walking,  in  which  the  four  limbs  always  take  part. 
Properly  speaking,  then,  the  hand  belongs  to  man  alone,  and 
its  conformation  does  not  permit  us  to  consider  it  as  a  nor- 
mal organ  of  locomotion.  It  can  by  turns  form  itself  into  a 
plane,  round  itself  into  a  cylinder,  hollow  itself  into  a  gutter^ 
make  the  fingers  spread  like  so  many  diverging  rays,  and 
form,  in  the  words  of  De  Blainville,  a  compass  with  five 
branches;  it  collects  the  fingers  in  the  form  of  a  cone,  of  a 


48  THE   HUMAN   BODY. 

spheroid,  &c.;  and  lastly,  it  can  reach  every  portion  of  the 
body. 

The  hand  is  essentially  the  organ  of  touch  and  of  prehen- 
sion. These  functions  devolve  principally  upon  its  anterior 
or  palmar  face.  The  nervous  papillae  with  which  it  is  pro- 
vided abound  specially  at  the  ends  of  the  fingers,  where  they 
form  furrows  in  elegant  curves  under  the  epidermis.  The 
tendons  in  it  are  very  numerous,  and  bound  together  by 
multiplied  connections.  Strong  aponeuroses  and  sheaths, 
through  which  the  tendons  slide,  make  the  skin  compact,  and 
combine  to  give  unity  to  the  general  movements  of  the  dif- 
ferent parts  of  the  organ,  and  independence  to  partial  ones. 
A  layer  of  adipose  tissue,  very  close  in  texture,  protects,  with- 
out lessening  its  power  or  its  delicacy,  that  network  of 
muscles,  vessels,  and  nerves,  this  apparatus  which  sometimes 
barely  touches  an  object,  and  sometimes  grasps  it  with  such 
violent  pressure.  The  hand,  in  fact,  is  either  a  delicate 
pincer  or  a  powerful  vice;  it  guides  the  burin  of  the  en- 
graver, which  leaves  behind  it  the  finest  trace,  the  hatchet 
of  the  carpenter  and  the  axe  of  the  woodman,  whose  blows 
are  given  with  as  much  strength  as  skill.  The  fingers  of  the 
sailor  knot  the  heavy  cordage,  and  those  of  the  optician 
stretch  a  spider's  thread,  without  breaking  it,  across  the  field 
of  an  astronomical  telescope.  The  same  organ  can  hold  a 
switch,  a  club,  a  sword,  a  hammer,  or  a  pen.  It  moulds 
itself  to  a  body  to  ascertain  its  form ;  it  comes  to  the  aid  of 
the  eye  in  completing  or  rectifying  its  impressions,  and  in 
some  cases  even  supplies  its  place.  Thus  the  finger  of  the 
physician  perceives  on  the  surface  of  an  organ  the  slightest 
inequality  in  relief;  and  the  hand  of  Michael  Angelo  fol- 
lowed with  enthusiasm  the  contour  of  the  antique  torso, 
which  the  eyes  of  the  great  artist  could  no  longer  contem- 
plate. 

But  nothing  gives  a  more  complete  idea  of  the  perfection 
of  the  mechanism  of  the  hand,  than  the  execution  of  instru- 
mental music.  Examine  an  artist  while  he  plays  on  a  violin. 
His  fingers  rest  upon  the  strings  so  as  to  leave  them  exactly 
of  the  length  necessary  for  the  tones  they  are  to  give.  The 
half  of  a  millimetre,  more  or  less,  greatly  changes  the  true- 


ACTIONS    OF   THE    HAND.  49 

ness  of  the  note;  and  a  cord  a  millimetre  out  of  place  pro- 
duces a  note  which  even  the  unpractised  ear  recognizes  as 
false.  But  the  fingers  fall  upon  the  strings  at  precisely  the 
point  required.  They  run  over  them,  succeeding  each  other 
with  giddy  rapidity,  following  every  imaginable  combination, 
and  yet  the  hand  gliding  over  the  instrument  incessantly 
changes  its  position.  Sometimes  a  single  finger  produces  an 
isolated  note;  sometimes  two  or  three  act  simultaneously  to 
produce  a  concord;  while  a  fourth,  striking  the  string  with 
increasing  rapidity,  produces  a  trill  which  rivals  that  of  the 
nightingale.  And  even  this  is  not  all.  The  other  hand 
holds  the  bow,  and  the  movements  of  the  right  arm  must  be 
in  correspondence  with  those  of  the  left  hand;  the  coincid- 
ence between  the  movements  of  one  hand  and  that  of  the 
other  must  be  mathematically  exact.  Add  to  these  all  the 
modifications  necessary  to  produce  the  piano  and  the  forte, 
to  swell  the  sound  or  to  let  it  die  away — all,  in  a  word,  that 
constitutes  musical  expression,  and  it  will  be  admitted  that 
this  mechanism  is  allied  to  the  wonderful,  and  that  it  sur- 
passes the  most  perfect  productions  of  human  art. 

The  agility  and  flexibility  of  the  hands,  the  concordance 
and  independence  of  their  movements,  is  not  less  remarkable 
in  the  playing  of  the  pianist.  How  is  it  possible  not  to  ad- 
mire those  two  hands,  both  oftenest  occupied  together,  and 
the  action  of  which  alternates  or  coincides  with  so  much  pre- 
cision and  rapidity;  together  they  produce  on  an  average  from 
six  to  eight  notes  at  a  time — separating,  approaching,  crossing, 
and  mingling  their  fingers,  which  move  over  the  keys  as  if  each 
one  were  completely  independent  of  all  the  others?  A  skil- 
ful pianist  produces  about  640  notes  a  minute  in  medium 
time,  and  960  in  extremely  quick  time.  These  numbers 
give  us  an  idea  of  the  rapidity  of  movement  which  can  be 
attained  by  the  hand  of  man. 

The  devoted  servant  of  the  body,  the  hand  which  nourishes 
it  knows  also  how  to  defend  it.  It  has  been  said  that  man 
is  created  without  arms.  What  then  is  the  hand  which  en- 
ables him  to  construct  and  employ  for  his  defence  those  in- 
genious and  terrible  machines,  that  hand  which  can  at  need 
itself  become  a  formidable  weapon?  The  poets  have  sung 

4 


So  THE  HUMAN  BODY. 

the  praises  of  Pollux  defending  his  own  life  and  that  of  his 
companions  with  the  arms  which  nature  gave  him  ;  but  if  we 
admire  Pollux  battling  with  the  Sicilian  giant,  we  turn  our 
eyes  from  the  arena  ensanguined  by  the  gauntlet  of  Enteilus. 
The  soldier  considers  it  an  honour  to  employ  with  skill  in 
the  defence  of  his  country  the  sword  which  she  has  intrusted 
to  him;  but  he  despises  the  arms  and  the  trade  of  the 
gladiator. 

The  principal  function  of  the  upper  limb  is  to  remove 
objects  from  the  body,  and  to  draw  them  to  it;  but  it  can 
also  remove  the  body  from  a  fixed  point,  or  approach  it  to 
one.  It  is  in  this  way  that  the  sailor  raises  himself  on  the 
rigging,  or  the  gymnast  on  the  trapeze ;  but  the  weight  of  the 
body  is  not  in  proportion  to  the  strength  of  the  limbs  which 
raise  it,  and  although  exercise  renders  this  effort  less  difficult 
by  increasing  the  power  of  the  muscles,  it  is  evident  that 
here  the  arm  performs  a  function  which  does  not  devolve 
upon  it  chiefly,  and  which  belongs  to  a  more  powerful  mem- 
ber, of  which  we  will  now  speak. 

Lower  or  abdominal  limb. — It  is  composed,  like  the  upper 
limb,  of  four  parts — the  hip,  thigh,  leg,  and  foot.  The  two 
bones  of  the  hip,  or  pelvic  bones,  articulate  together  and  with 
the  sacrum;  this  last,  placed  between  the  two  like  a  wedge, 
transmits  by  their  means  the  weight  of  the  body  to  the  lower 
limbs,  which  are  the  pillars  of  the  human  edifice.  On  the 
external  face  of  each  pelvic  bone  we  see  a  deep,  hemispheri- 
cal, articular  cavity.  This  is  the  cotyloid  cavity,  which  receives 
the  head  of  the  thigh-bone,  and  forms  with  it  the  articulation 
of  the  hip.  The  femur  or  thigh-bone  is  the  longest  and 
strongest  bone  in  the  skeleton ;  it  is  almost  cylindrical,  and 
is  curved  outward,  which  gives  it  greater  strength.  At  its 
upper  extremity  we  see  the  head  of  the  femur,  supported  by 
a  neck  which  is  united  to  the  body  of  the  bone  at  an  ob- 
tuse "angle.'  This  obliquity  has  the  effect  of  increasing  the 
distance  between  the  two  femurs,  and  in  consequence  be- 
tween the  two  lower  extremities,  thus  giving  to  the  body  a 
larger  base  and  greater  stability.  Another  result  is,  that  the 
weight  of  the.  body  is  transferred  to  the  femur,  but  not 
directly  and  in  a  right  line;  the  necks  of  the  two  femurs 


HIP-JOINT,    KNEE-JOINT.  5! 

form  by  their  union  part  of  an  arch  upon  which  rests  the 
upper  portion  of  the  cotyloid  cavity,  and  thus  divides  the 
force  acting  upon  the  lower  limbs. 

The  head  of  the  femur  represents  nearly  two-thirds  of  a 
sphere.  It  exactly  fills  the  cotyloid  cavity,  but  is  not  itself 
all  inclosed  in  it,  as  the  depth  of  the  cavity  does  not  exceed 
half  the  diameter  of  the  sphere  to  which  it  belongs.  A  very 
elastic,  circular,  fibro-cartilaginous  ring  surrounds  the  edge 
of  the  cotyloid  cavity,  increasing  its  size,  embracing  the  head 
of  the  femur;  and  acts  as  a  valve  and  hermetically  closes  the 
articular  cavity  in  which  the  head  of  the  femur  is  retained  by 
atmospheric  pressure  alone.  In  fact,  if  we  place  this  articu- 
lation, properly  prepared,  under  the  receiver  of  an  air-pump, 
we  shall  see,  as  a  vacuum  is  produced,  the  head  of  the 
femur  gradually  slip  down  and  leave  the  cotyloid  cavity  as 
far  as  the  ligaments  will  permit,  and  when  air  is  again  ad- 
mitted into  the  receiver,  it  resumes  its  place  in  the  cavity. 
This  beautiful  experiment  of  E.  Weber  shows  in  a  striking 
manner  the  direct  and  constant  influence  of  external  agents 
on  the  functions  of  the  organism. 

The  inclosing  of  the  head  of  the  femur  in  the  cotyloid 
cavity  gives  the  articulation  of  the  hip  great  solidity,  which 
is  augmented  by  the  muscles  and  ligaments  which  hold  the 
parts  together  as  well  as  give  them  motion,  so  that  it  is  only 
by  the  greatest  violence  that  the  head  of  the  femur  can  be 
forced  out  of  this  cavity.  This  articulation,  which  is  of  the 
same  nature  as  that  of  the  shoulder,  permits  the  movement 
of  the  lower  limb  in  every  direction,  though  to  a  less  ex- 
tent than  that  of  the  arm.  We  shall  again  have  occasion  to 
discuss  this  movement. 

The  lower  extremity  of  the  femur  ends  in  two  oblong, 
rounded  masses,  which  are  called  the  condyles  of  the  femur, 
which  rest  in  two  cavities  in  the  superior  portion  of  the  princi- 
pal bone  of  the  leg,  or  tibia,  and  form  with  them  the  articula- 
tion of  the  knee.  The  semi-lunar  cartilages,  in  terposed  between 
the  two  bones,  diminish  the  pressure  of  the  femur  on  the 
tibia,  and  prevent  the  displacement  of  the  former  by  increas- 
ing the  surface  and  depth  of  the  articular  cavity.  In  front 
of  the  knee-joint  is  placed  fas  patella  or  knee-pan,  the  largest 


S3  THE    HUMAN    BODY. 

of  the  sesamoid  bones,  which  adapts  itself  by  two  articular 
facets  to  those  presented  by  the  condyles  of  the  femur,  and 
gives  attachment  by  its  upper  border  to  the  tendon  of  the 
extensors  of  the  leg,  while  by  its  lower  border  it  is  intimately 
united  to  the  ligament  of  the  knee-pan,  which  fastens  it  to 
the  tibia.  In  comparing  the  elbow  with  the  knee,  we  per- 
ceive the  striking  similarity  of  the  knee-pan  to  the  olecranon. 
The  knee-pan  serves  as  a  pulley  for  the  extensor-muscles,  the 
action  of  which  upon  the  leg  is  increased  by  the  change  of 
direction  given  to  them,  while  the  olecranon  is  a  powerful 
lever,  by  means  of  which  the  fore-arm  is  extended. 


Fig.  17. — Knee-joint. 

Front  view.  Side  view. 

A.  Femur.  A.  Femur. 

D,  t>.    Condyles  of  femur.  B.  Knee-pan. 

d.   Upper  extremity  of  fibula.  C.   Tibia. 

C.  Tibia.  D.  Fibula. 

D.  Fibula. 

The  second  bone  of  the  leg  is  \hefibula,  which  is  parallel 
to  the  tibia,  and  with  it  forms  the  articulation  of  the  foot. 
This  bone,  which  takes  no  part  in  the  articulation  of  the 
knee,  yet  represents  the  ulna,  which  plays  so  important  a 
part  in  the  formation  of  the  elbow,  while  the  tibia  corre- 


ANKLE-JOINT.  53 

spends  to  the  radius.  Nature,  by  one  of  those  transforma- 
tions of  which  she  furnishes  numerous  examples,  has  united 
the  two  extremities  of  the  ulna  and  radius  in  one,  allowing 
the  first  of  these  bones  to  exist  only  as  a  rudiment  in  its  upper 
portion.  This  blending  of  two  organs  is  termed  by  naturalists 
a  coalescence.  The  resemblance  of  the  tibia  to  the  radius 
was  remarked  by  De  Blainville,  and  has  been  demonstrated 
by  M.  Martins  in  his  beautiful  work  on  the  pelvic  and 
thoracic  limbs. 

The  lower  extremities  of  the  tibia  and  fibula  united  form 
a  mortise,  in  which  the  astragalus,  one  of  the  bones  of  the 
tarsus,  is  received,  and  thus  constitute  the  tibio-tarsal  articula- 
tion, or  articulation  of  the  foot.  The  foot  moves  upon  the  leg 
in  such  a  manner  as  to  form  with  it  a  straight  line  when 
extended.  The  movement  in  an  opposite  direction,  or  flexion, 
is  much  more  limited,  the  two  mallcoli  which  embrace  the 
astragalus  not  permitting  lateral  movements  in  the  foot,  those 
which  do  take  place  being  made  by  the  articulation  of  the 
astragalus  with  the  other  parts  of  the  tarsus,  though  a  limited 
movement  of  circumduction  can  be  made  by  the  foot. 

It  has  been  said  that  the  foot  is  another  hand — -pes  alter  a 
manus — and  if  the  hand  completes  the  arm,  so  does  the  foot 
complete  the  leg.  Without  it  locomotion  could  not  be 
effected  except  by  movements  quite  different  from  those  of 
walking,  and  under  conditions  of  equilibrium  much  less 
favourable,  and  with  much  greater  fatigue;  running,  and 
consequently  jumping,  would  be  impossible.  But  if  the  foot 
and  the  hand  are  varieties  of  the  same  type  of  organization, 
they  present  differences  in  regard  to  their  respective  uses; 
the  foot,  designed  to  support  the  body,  is  especially  remark- 
able for  its  solidity;  in  the  hand  mobility  is  the  predomi- 
nating quality. 

The  foot  of  man,  exclusively  designed  for  the  support  of 
the  body,  is  not  an  organ  of  prehension,  and  cannot,  like  the 
foot  of  the  monkey,  take  hold  of  objects  by  opposing  the 
thumb  to  the  other  fingers ;  the  toes,  disposed  upon  the  same 
plane,  have  neither  the  length  of  the  fingers  nor  the  extent 
and  variety  of  their  movements;  in  a  word,  it  is  a  foot  and 
not  a  hand,  as  it  is  in  the  quadrumana. 


54 


THE    HUMAN    BODY. 


The  foot  is  composed  of  twenty-six  bones,  seven  of  which 
constitute   the   tarsus,  which  articulates  with  the  leg  and 


Fig.  18. — Skeleton  of  the  foot. 

A.  Internal  malleolus,  lower  ex tr em-         E.  Cuboid, 
ity  of  tibia. 

B.  Astragalus. 

C.  Calcaneum. 

D.  Scaphoid. 


F.  First  metatarsal. 

G,  H.  First  and  second  phalanx  of  the 
great  toe. 


corresponds  to  the  carpus.  Five  bones  form  the  metatarsus, 
which  corresponds  to  the  metacarpus,  and  articulates  with 
the  tarsus  behind  and  with  the  toes  in  front.  The  foot  is 
narrow  and  thick  in  its  posterior  part,  thinner  and  broader 
anteriorly ;  it  forms  a  right  angle  with  the  leg,  and  rests  upon 
the  ground  at  the  extremities  only.  The  middle  portion  is 
in  the  form  of  an  arch,  and  in  consequence  resists  shocks 
and  supports  pressure  much  better  than  it  could  if  it  were 
flat  and  touched  the  ground  throughout  its  whole  length. 
And  although  the  parts  are  very  firmly  united  together,  there 
is  sufficient  mobility  to  give  great  elasticity  to  the  whole,  and 
this  elasticity  is  augmented  by  the  toes.  The  foot  thus 
supports  the  weight  of  the  body  like  an  arch  and  spring 
combined,  giving  it  in  this  way  great  advantage  in  resistance. 
And  lastly,  in  jumping  from  a  height  it  extends  itself 
instinctively,  and  touches  the  earth  first  at  its  point  only,  so 
as  to  break  the  shock.  This  distribution  of  force,  which 
results  from  the  form  and  the  elasticity  of  the  foot,  not  only 


UPPER    AND    LOWER    LIMBS. 


55 


protects  its  mechanism,  but  also  avoids  the  grave  injuries 
which  might  be  produced  in  certain  organs,  such  as  the  brain 
and  the  liver,  by  the  rebound. 


Fig.  19.— The  foot. 

If  we  compare  the  upper  and  the  lower  limbs  taken  as  a 
whole,  we  shall  remark  among  their  principal  distinguishing 
characteristics,  that  the  flexion  of  the  fore-arm  upon  the  arm 
takes  place  in  a  forward  direction,  while  that  of  the  leg  is 
backward.  M.  Martins  has  demonstrated  that  this  opposi- 
tion in  their  movements,  necessitated  by  their  destination  to 
different  functions,  is  due  to  the  twisting  of  the  humerus. 
The  femur  is  a  straight  bone  and  not  twisted  upon  its  axis. 
The  humerus,  on  the  contrary,  is  turned  on  itself  180°,  or 
half  the  circumference.  This  is  not  the  result  of  the  me- 
chanical action  of  the  muscles  and  of  the  function  of  the 
upper  limb ;  although  the  form  of  the  bone  does  not  permit 
this  peculiarity  to  be  anatomically  recognized  till  about  the 
second  year,  it  exists  virtually  as  soon  as  the  bone  is 
developed.  Muscles,  vessels,  and  nerves  all  follow  this 
rotating  movement  indicated  by  the  spiral  disposition  of  the 
humerus,  and  most  anatomists  have  pointed  it  out  without 
hinting  at  the  physiological  consequences  which  M.  Martins 
has  shown  result  from  it.  This  learned  observer  has  shown 
that  the  humerus,  artificially  untwisted,  corresponds  in  all 
points  with  the  femur  of  the  same  side,  and  by  this  manoeuvre 


56  THE    HUMAN    BODY. 

in  an  opposite  direction  to  the  work  of  nature,  he  has 
explained  the  proceeding  by  which  she  bent  the  articulation 
of  the  elbow  forward  and  that  of  the  knee  backward. 

The  articulations  of  the  lower  limb  permit  to  it  a  great 
variety  and  extent  of  movement.  Under  the  action  of 
powerful  muscles  it  folds  back  upon  itself  or  becomes  a 
rigid  column,  raising  or  lowering  with  rapidity  and  facility 
the  body  of  which  it  supports  the  weight.  In  walking  it  is 
carried  forward  or  backward,  and  by  turns  extended  or  bent; 
it  turns  on  its  axis  or  changes  from  the  vertical  in  order  to 
maintain  the  equilibrium  by  the  direction  of  the  foot  or  to 
enlarge  the  base  of  support.  It  can  raise  itself  laterally  almost 
to  a  right  angle  with  the  body,  and  in  front  it  approaches  it 
still  more  nearly.  In  fencing  it  bends  or  is  extended,  raises 
and  lowers  the  body,  and  carries  it  backward  and  forward  by 
movements  which  succeed  each  other  almost  as  rapidly  as 
those  of  the  arms.  But  it  is  especially  in  the  varying  steps 
of  a  skilful  dancer  that  we  can  admire  the  perfection  of  this 
mechanism,  and  all  the  suppleness,  strength,  and  agility  that 
exercise  can  give  to  it. 


CHAPTER  V. 


Motion. — Effort. — Locomotion;    standing,   walking,    running,  jumping, 
swimming. 

Motion. — Physiologists  remark  several  varieties  of  motion 
which  may  be  grouped  in  two — voluntary  and  involuntary 
movements.  Among  the  involuntary  movements,  which  ars 
also  called  automatic,  some  result  from  the  impression  pro- 
duced by  an  idea,  a  passion,  or  a  scene,  gay  or  sad,  or  by  a 
movement  identical  with  that  which  is  produced.  Such  art, 
laughing,  and  the  motions  of  the  face  expressing  sadness, 
anger,  fear,  and  other  moral  or  physical  impressions;  trem> 
bling  of  the  limbs  in  consequence  of  deep  emotion,  yawning, 
and  so  forth.  Others  proceed  from  the  excitement  of  ths, 
sensitive  nerves,  such  as  sneezing,  coughing,  winking,  chat- 
tering of  the  teeth,  or  shivering  after  a  cold  bath. 

In  certain  cases,  in  fact,  impressions  transmitted  from  th& 
organs  to  the  brain,  either  directly  by  the  nerves  of  sensa- 
tion or  indirectly  by  the  spinal  cord,  without  any  sensation 
taking  place,  or  what  amounts  to  the  same  thing,  without 
our  being  conscious  of  any,  occasion  an  excitement  which  is 
transmitted  to  the  motor-nerves,  and  causes  movements  in 
which  the  will  has  no  part.  These  movements  are  generally 
executed  by  the  muscles  of  organic  life,  which  are  not 
under  the  control  of  the  will ;  but  they  can  also  be  made  by 
those  which  are  under  its  control.  These  are  called  reflex 
movements.  Some  of  them  are  undoubtedly  automatic;  as 
for  the  others,  it  has  not  been  demonstrated  that  a  sensation 
and  an  act  of  the  will  do  not  precede  the  muscular  contrac- 
tion. Thus  sneezing  and  coughing  are  independent  of  the 


58  THE    HUMAN    BODY. 

will,  it  can  neither  prevent  them  nor  arrest  their  develop- 
ment. It  is  the  same  with  the  chattering  of  the  teeth,  with 
shivering  and  winking  of  the  eyelids  on  contact  with  the  air, 
with  the  tears,  or  only  when  a  foreign  body  menaces  the  eye. 
In  this  last  case,  although  the  muscular  contraction  is  in- 
stantaneous and  seems  to  be  involuntary,  it  is  evidently  pre- 
ceded by  a  sensation  which  the  eye  has  transmitted  to  the 
brain.  This  may  even  be  considered  as  voluntary,  since  if 
the  attention  is  excited,  the  will  can  oppose  the  instinctive 
movement. 

Other  movements  take  place  in  the  organism  of  which  we 
have  more  or  less  perception;  when  a  carriage  threatens  to 
overset,  for  example,  we  throw  ourselves  to  the  side  opposite 
the  inclination ;  or  when  suddenly  coming  on  the  edge  of  a 
precipice  the  body  stiffens  or  is  thrown  backward;  and  when 
a  player  at  ball  or  billiards  inclines  or  turns  in  the  same  direc- 
tion in  which  he  wishes  to  direct  his  ball.  Analogous 
phenomena  are  caused  by  a  sort  of  attraction  or  instinctive 
imitation.  When,  for  example,  the  eyes  follow  the  move- 
ment of  a  great  waterfall  into  a  gulf,  the  body  very  soon  fol- 
lows the  oscillations,  though  we  do  not  perceive  them  until 
the  motion  becomes  so  great  as  to  threaten  to  drag  us  into 
the  abyss.  We  are  indebted  to  M.  Chevreul  for  the  obser- 
vation and  explanation  of  effects  of  this  nature,  of  which 
charlatanism  avails  itself  in  table-turning.  If  the  elbow  be 
placed  upon  a  table,  and  a  pendulum  formed  of  a  string  and 
a  ring  be  held  in  the  hand,  and  we  fix  the  eyes  on  the  ring, 
we  shall  soon  see  it  begin  to  oscillate,  although  the  arm  ap- 
parently remains  immovable;  the  oscillations  may  keep  the 
same  direction,  or  change  according  to  the  mental  desire, 
and  this  without  any  bad  faith  or  a  consenting  movement  on 
the  part  of  the  person  holding  the  pendulum.  But  if  we 
place  a  support  under  the  hand  near  the  end  of  the  fingers, 
or  a  bandage  over  the  eyes  of  the  experimenter,  the  oscilla- 
tions cease.  They  were  caused  by  an  almost  imperceptible 
and  involuntary  movement  of  the  fore-arm  and  hand,  under 
the  influence  of  the  eyes  looking  at  the  ring  and  the  direc- 
tion that  it  takes.  And  again  it  is  a  similar  movement  or 
series  of  movements  which  gives  the  impulse  to  the  turning 


VOLUNTARY  MOTION EFFORT.  59 

table;  in  the  unconsciousness  of  the  muscular  contraction 
lies  all  the  merit  of  this  phenomenon,  which  loses  its  mar- 
vellous character  as  soon  as  you  show  the  too  credulous  per- 
formers that  they  themselves  are  the  involuntary  movers. 

Voluntary  movements,  as  their  name  indicates,  are  produced 
under  the  influence  of  the  will,  but  not  under  its  direct  or 
immediate  action.  The  volition  of  the  movements  of  loco- 
motion, for  example,  emanate  from  a  certain  part  of  the 
brain,  from  the  cerebral  lobes;  but  in  order  that  the  move- 
ment may  be  executed,  the  muscles  must  contract,  and  this 
muscular  contraction  owes  its  origin  to  a  force  which  ema- 
nates from  the  occipital  protuberance,  a  different  part  of  the 
brain  from  that  which  gives  birth  to  thought.  Observations 
on  paralytics  prove  that  the  will  is  insufficient  to  produce 
movement. 

In  order  that  movements  may  be  executed  in  the  order 
and  with  the  unity  necessary  to  the  accomplishment  of  the 
will,  they  must  be  co-ordinate.  Several  physiologists,  and 
especially  Flourens,  have  regarded  the  cerebellum  as  the 
organ  essential  to  this  co-ordination  of  movement.  A  lesion 
of  this  part  of  the  brain  produces  a  disturbance  in  locomo- 
tion similar  to  that  caused  by  drunkenness ;  but  pathological 
observation  has  demonstrated  that  there  is  sometimes  absence 
of  co-ordination  when  the  cerebellum  is  not  affected. 

The  muscles  unite  in  the  voluntary  movements,  some  as 
motors,  and  others,  antagonistic  to  these,  as  the  moderators 
of  movement.  M.  Duchenne  (of  Boulogne)  has  shown  that 
in  the  voluntary  movements  of  the  limbs  and  the  trunk  these 
two  systems  of  muscles,  impulsive  and  modifying,  are  simul- 
taneously contracted  by  a  double  nervous  excitation;  one  to 
produce  the  movement  and  the  other  to  modify  it.  Without 
this  unity  of  intention  between  the  antagonistic  muscles,  the 
movements  would  lose  their  precision  and  their  certainty. 

Effort. — When  one  or  several  groups  of  muscles  contract 
themselves  strongly  in  order  to  perform  a  function  requiring 
force,  or  to  overcome  an  obstacle,  to  draw  or  push  away  a  • 
body,  the  name  effort  has  been  given  to  this  action  of  the 
muscles.  There  is  effort  in  walking,  climbing,  running,  and 
a  great  number  of  other  functions.  Whatever  muscles  take 

\ 


60  THE   HUMAN    BODY. 

part  in  effort  they  must  have  a  point  of  support  or  fulcrum, 
directly  or  indirectly  upon  the  skeleton  of  the  trunk,  that  is 
on  the  spinal  column  and  the  bones  of  the  thorax.  An  effort 
is  always  preceded  by  an  inspiration  which  dilates  the  thorax, 
thus  rendering  the  bones  of  which  it  is  composed  immovable 
by  the  contraction  of  the  inspiratory  muscles,  and  furnishing 
a  fixed  point  to  the  muscles  attached  to  these  bones.  Thus, 
one  after  another,  the  greater  part  of  the  muscles  of  the 
system  joins  in  a  movement  of  which  sometimes  the  arm  or 
the  hand  only  is  the  immediate  instrument.  The  proof  of 
this  is  the  impossibility  of  making  a  movement  distinct  from 
that  which  is  the  immediate  object  of  the  effort,  without  this 
effort  ceasing  or  diminishing.  When  it  is  at  its  highest  point, 
respiration  is  suspended,  the  glottis  closes  or  remains  slightly 
open,  according  to  the  nature  and  the  degree  of  intensity  in 
the  effort ;  the  inspired  air  distends  the  lungs,  and  if  a  part 
escapes  it  is  too  small  to  lessen  the  expansion  of  the  chest; 
the  abdominal  viscera  are  compressed  from  above  by  the 
diaphragm  in  front,  and  laterally  by  the  muscles  of  the  abdo- 
men. During  certain  efforts  the  air  is  expelled  slowly  through 
the  glottis,  and  when  the  movement  terminates  suddenly 
with  redoubled  force,  the  expiration  is  accomplished  rapidly 
and  sometimes  in  the  form  of  a  cry.  The  sailor  who  hauls 
in  a  rope,  or  the  baker  as  he  with  difficulty  raises  the  dough 
to  throw  it  back  into  the  kneading-trough,  accompanies  the 
movements  which  he  executes  with  a  cry  of  which  the  rhythm 
expresses  the  different  periods  of  the  effort. 

Locomotion. — Man  moves  over  the  surface  of  the  ground 
by  three  principal  methods  of  progression — walking,  running, 
and  leaping ;  but  the  point  of  departure  is  always  the  vertical 
position.  In  this  attitude,  which  characterizes  the  human 
race,  the  equilibrium  of  the  head  upon  the  vertebral  column, 
and  that  of  the  trunk  upon  the  coxo-femoral  articulations, 
and  of  the  thighs  on  the  legs,  is  independent  of  all  muscular 
contraction,  the  ligaments  being  sufficient  to  insure  it.  And 
farther,  the  muscles  of  the  neck,  of  the  trunk,  and  of  the 
thigh  maintain  the  rigidity  of  the  spinal  column,  oppose  or 
prevent  the  flexion  of  the  knee,  and  restore  the  equilibrium 
when  it  is  compromised,  while  the  muscles  of  the  leg  prevent 


THE    ERECT    POSITION. 


61 


the  flexion,  anterior  or  posterior,  of  the  tibio-tarsal  articula- 
tion, the  surfaces  and  ligaments  of  which  only  permit  an  un- 
stable equilibrium  of  the  body  upon  the  feet.  Lastly,  the 
feet,  separated  from  each  other  by  a  distance  equal  to  that 


Fig.  20. — The  leg  in  standing. 

The  foot  resting  the  toes  on  The  foot  resting  flat  on  the  ' 

the  ground.  ground. 

which  divides  the  heads  of  the  femurs,  complete  the  mechan- 
ism by  which  man  alone,  among  all  living  beings,  stands 
erect  with  his  face  placed  vertically,  and  on  a  plane  parallel 
to  that  of  the  body,  but  not  turned  toward  heaven,  as  has 
been  poetically  said. 

In  the  attitude  of  a  soldier  without  arms,  with  the  heels 
touching  each  other,  and  the  feet  forming  nearly  a  right 
angle,  a  stronger  contraction  of  the  muscles  of  the  leg  is 


62  THE    HUMAN    BODY. 

necessary,  and  consequently  fatigue  is  sooner  induced.  When 
resting  on  one  foot  only  the  body  departs  laterally  from  the 
vertical  and  leans  a  little  backward,  the  leg  which  supports 
only  its  own  weight  rests  on  the  ground,  with  the  muscles 
completely  relaxed,  acting  as  a  support  and  counterpoise. 
This  attitude  when  standing  is  the  least  fatiguing,  firmest, 
and  also  the  most  elegant;  it  is  the  one  preferred  by  painters 
and  sculptors,  and  was  considered  by  Leonardo  de  Vinci  as 
the  most  natural. 

When  the  body  moves  it  is  divided  into  two  quite  distinct 
sections:  the  one,  comprising  the  head,  trunk,  and  upper 
limbs,  representing  the  mass  to  be  transported;  the  lower 
limbs  are  at  once  the  movable  supports  of  the  superior  parts 
of  the  body,  and  the  agents  of  propulsion  which  communi- 
cate to  them  the  movement  of  translation.  In  all  move- 
ments of  this  nature  the  trunk  inclines  forward  at  an  angle 
which  varies  according  to  the  quickness,  from  5°  7'  in  the 
slowest  walk  to  22°  5'  in  the  fastest  running.  From  this 
position  there  is  a  constant  tendency  to  fall  forward,  which 
is  neutralized  by  the  moving  of  the  lower  limbs  in  such  a 
direction  as  that  the  heads  of  the  femurs  shall  always  serve 
as  the  point  of  support  for  the  body.  M.  Longet  compares 
this  unstable  equilibrium  of  the  body  upon  the  femurs  to 
that  of  a  rod  on  the  end  of  a  finger,  so  inclined  that  the 
only  means  to  prevent  its  fall  is  to  carry  the  finger  forward 
in  the  same  direction  as  the  inclination,  more  rapidly  as  this 
inclination  becomes  greater. 

By  their  alternate  flexion  and  extension  the  lower  ex- 
tremities give  an  impulsion  to  the  trunk,  they  lengthen  and 
contract  in  a  direction  inclined  to  the  horizon,  since  it  is 
forward  and  not  vertically  that  they  push  the  body;  the  re- 
sult is  that  the  centre  of  gravity  sinks  toward  the  ground  just 
in  proportion  to  the  rapidity  of  the  mode  of  progression. 

Each  extremity  props  itself  by  turns  on  the  ground,  and 
then  the  impulse  being  given  the  knee  bends,  the  heel  rises, 
the  foot  is  lifted,  the  limb,  shortened  by  flexion  and  sus- 
pended from  the  pelvis,  is  directed  from  behind  forward, 
and  is  again  placed  upon  the  ground. 

In   this   movement   the   leg,  according   to  the  brothers 


WALKING.  63 

Weber,  represents  a  pendulum  which  bends  and  oscillates 
by  its  weight  alone;  according  to  M.  Duchenne  (of  Bou- 
logne), it  obeys  the  contraction  of  the  flexor-muscles. 

The  experiments  of  the  Webers  having  demonstrated, 
as  stated  above,  that  the  head  of  the  femur  is  retained 
in  the  cotyloid  cavity  by  atmospheric  pressure  alone,  these 
skilful  observers  conclude  that  in  the  second  movement  in 
walking  the  weight  of  the  thigh  alone  determines  the  flexion 
of  the  joints  and  the  oscillation  of  the  three  segments  of  the 
pendulum,  which  is  then  represented  by  the  lower  extremity. 
Basing  his  opinion  on  pathological  observation,  M.  Duchenne 
thinks  that  the  contraction  of  the  flexors  of  the  thigh,  leg, 
and  foot  is  the  real  cause  of  the  second  movement  of  the 
extremity  in  walking,  and  that  the  action  of  weight  contri- 
butes very  little  to  it.  According  to  M.  Beclard,  the  tonicity 
of  the  flexor-muscles,  developed  by  extension,  suffices  for 
seconding  the  pendulum  movement  of  the  lower  limb. 

In  walking  the  body  advances  without  ceasing  to  rest 
upon  the  ground,  and  by  effecting  a  succession  of  move- 
ments, which  are  divided  in  each  step  into  two  principal 
ones.  First, — the  body  rests  upon  the  two  lower  limbs ;  the 
right  leg,  placed  behind  and  inclined  to  the  horizon,  touches 
the  ground  at  the  extremity  of  the  metatarsus  and  at  the 
toes,  it  stretches  out,  and  the  foot  is  raised  to  an  angle  of 
forty-five  degrees;  now  the  left  limb  is  placed  forward,  rest- 
ing on  the  ground  on  its  sole,  the  knee  is  a  little  bent,  the 
heel  exactly  under  the  head  of  the  femur,  and  the  trunk 
slightly  inclined  forward.  Secondly, — the  left  leg  alone  sup- 
ports the  weight  of  the  body;  it  lengthens  by  extending  the 
knee  and  straightening  the  foot;  its  direction  inclines  to  the 
horizon,  and  the  body  pushes  itself  forward,  while  the  right 
leg  is  raised  from  the  ground  by  bending  the  knee,  follows 
the  movement  of  translation  given  to  the  body,  executes 
half  an  oscillation,  and  touches  the  ground,  first  at  the  heel, 
which  places  itself  exactly  under  the  head  of  the  femur,  and 
then  on  the  sole  of  the  foot  on  which  the  body  rests. 

To  accelerate  his  movement  man  inclines  more  forward, 
the  centre  of  gravity  falls  nearer  to  the  earth,  and  the  flexion 
of  the  limb  placed  behind  is  greater,  the  pendulum  is  shorter 


64  THE    HUMAN    BODY. 

and  its  oscillation  more  rapid;  at  the  same  time  the  greater 
flexion  gives  more  force  to  the  extension,  and  the  impulsion 
forward  is  increased;  and  more  still,  extension  acts  in  a  direc- 
tion still  more  inclined,  which  results  in  a  lengthening  of 
the  step.  The  motion  is  also  increased  by  the  extension  of 
the  leg  resting  on  the  ground  while  the  other  oscillates,  in 
such  a  way  that  when  the  latter  touches  the  ground  the 
former  detaches  itself  in  order  to  swing  in  its  turn.  In 
walking  quickly  the  body  rests  upon  the  ground  only  by  one 
foot  at  a  time. 

When  walking,  and  especially  when  walking  rapidly,  the 
arms  accompany  with  their  isochronous  oscillations  the 
movements  of  the  lower  limbs,  and  contribute  to  maintain  the 
equilibrium:  indeed  it  is  next  to  impossible  to  walk  quickly 
when  the  arms,  from  any  cause  whatever,  cannot  oscillate. 

According  to  the  experiments  of  the  brothers  Weber,  the 
speed  of  a  man  of  ordinary  stature  is,  in  rapid  walking,  about 
10,267  yards  per  hour.  This  speed  could  not  long  be  main- 
tained, and  must  be  considered  as  exceptional.  In  ordinary 
walking  the  speed  is  nearly  four  miles  an  hour,  and  can 
be  kept  up  for  a  long  period  But  exercise  and  a  special 
aptitude  for  it  enable  some  men  to  walk  great  distances  in  a 
relatively  short  space  of  time.  Trained  walkers  have  gone 
seventy-five  miles  in  twenty  hours,  and  walked  the  distance  of 
thirty-seven  miles  at  the  rate  of  five  miles  an  hour.  The  moun- 
taineers of  the  Alps  are  generally  good  walkers,  and  some 
of  them  are  not  less  remarkable  for  endurance  than  for 
speed.  Jacques  Balmat,  who  was  the  first  to  reach  the  sum- 
mit of  Mont  Blanc,  at  sixteen  years  of  age  could  walk  from 
the  hamlet  of  the  Pe'lerins  to  the  mountain  of  La  Cote  in 
two  hours — a  distance  which  the  best  trained  travellers  re- 
quired from  five  to  six  hours  to  get  over.  At  the  time  of 
his  last  attempt  to  reach  the  top  of  Mont  Blanc,  this  same 
guide,  then  twenty  years  old,  passed  six  days  and  four  nights 
without  sleeping  or  reposing  a  single  moment.  One  of  his 
sons,  Edward  Balmat,  left  Paris  to  join  his  regiment  at 
Genoa;  he  reached  Chamonix  the  fifth  day  at  evening, 
having  walked  340  miles.  After  resting  two  days  he 
set  off  again  for  Genoa,  where  he  arrived  in  two  days. 


WALKING — TROTTING.  65 

Several  years  afterward  this  same  man  left  the  baths  at 
Loueche  at  two  o'clock  in  the  morning,  and  reached  Cha- 
monix-  at  nine  in  the  evening,  having  walked  a  distance 
equal  to  about  seventy-five  miles  in  nineteen  hours.  In  1844 
an  old  guide  of  De  Saussure,  eighty  years  old,  left  the  hamlet 
of  Prats  in  the  valley  of  Chamonix  in  the  afternoon,  and 
reached  the  Grands  Mulets  at  ten  in  the  evening,  then  after 
resting  some  hours  he  climbed  the  glacier  to  the  vicinity  of 
the  Grand  Plateau,  which  has  an  altitude  of  about  13,000 
feet,  and  then  returned  without  stopping  to  his  village. 

We  will  cite  in  addition  the  performance  of  a  man  from 
Thun,  who  walked  in  September,  1867,  a  distance  estimated 
at  forty  Swiss  leagues  in  twenty-three  hours,  representing  at 
least  thirty-four  hours  of  walking  for  ordinary  travellers. 

Running  differs  from  walking  principally  in  the  fact  that 
at  a  given  moment  the  body  leaves  the  ground,  and  passes 
through  space  in  the  same  manner  as  a  projectile.  The 
body  is  inclined  more  forward,  and  the  centre  of  gravity  is 
lower  than  when  walking.  The  lower  limbs  execute  the 
same  alternate  movements  as  in  the  first  mode  of  progres- 
sion; but  at  the  moment  when  the  right  leg  leaves  the 
ground  and  commences  its  demi-oscillation,  the  left,  which 
is  bent  and  only  touches  the  ground  at  the  extremity  of  the 
foot,  pushes  rapidly  forward,  and  with  sufficient  force  to 
throw  the  body  upward  and  forward,  and  the  two  legs  oscil- 
late together  during  an  instant,  then  the  one  which  left  the 
ground  first  falls  before  the  other  on  the  point  of  the  toes. 
The  body  has  made  a  spring,  and  the  same  manoeuvre  takes 
place  alternately  on  each  side,  and  the  result  is  a  succession 
of  springs  which  constitute  running. 

Trotting  is  running  when  the  impulsion  forward  is  not  so 
strong,  and  the  movements  are  less  rapid,  which  renders  it 
more  applicable  to  uneven  ground,  where  it  is  necessary  to 
choose  the  place  where  the  foot  is  to  be  placed  at  each  step. 

The  greatest  attainable  speed  for  a  man  is,  according  to 
the  brothers  Weber,  seventeen  miles  in  an  hour;  but  if  this 
speed  has  ever  been  maintained  for  one  hour,  which  is 
doubtful,  it  could  not  certainly  be  continued  much  longer. 
The  maximum  of  speed  attained  in  the  gymnasium  of 


66  THE    HUMAN    BODY. 

Amoros  was  twenty-five  miles  in  two  hours  and  forty-five 
minutes,  that  is,  about  nine  miles  an  hour. 

Leaping  is,  properly  speaking,  nothing  but  a  step  of  run- 
ning taken  singly.  A  man  can  jump  with  his  feet  joined, 
that  is  to  say,  the  two  feet  quit  the  ground  at  the  same  in- 
stant, and  the  body  is  thrown  vertically  upward  and  forward, 
or  backward.  The  jump  may  be  preceded  by  running  seve- 
ral steps  in  order  to  get  under  way,  as  it  is  termed.  In  this 
case  the  speed  acquired  during  the  first  steps  is  added  to  the 
impulse  given  to  the  body  by  the  last  one.  By  exercise 
men  have  succeeded  in  jumping  vertically  a  height  of  two 
metres,  and  horizontally  over  a  space  of  five  or  six  metres. 
Amoros  speaks  of  an  Englishman  who  jumped  across  a  ditch 
ten  metres  in  width. 

Swimming. — Man  can  sustain  himself  upon  the  water,  and 
traverse  it  for  a  considerable  space  by  swimming;  but  this  is 
not  an  instinctive  method  of  locomotion  for  him — he  must 
learn  to  swim,  while  walking  and  the  other  modes  of  pro- 
gression are  natural  to  him,  and  are  not  acquired  by  study. 
Man  walks,  runs,  and  jumps  just  as  an  amphibious  animal 
swims  without  having  learned  to  do  so;  but  to  swim  he  must 
study  the  attitudes  and  the  movements  which  neutralize  the 
effect  of  his  specific  gravity,  which  prevent  him  from  sinking 
into  the  water,  and  permit  him  to  gain  a  resting-point  in 
order  to  displace  it. 

The  quadruped  swims  as  if  walking  in  the  water,  that  is, 
by  making  just  the  same  movements  as  in  walking  on  the 
ground.  Man  can,  it  is  true,  swim  as  animals  walk,  striking 
the  water  with  his  four  members ;  but  he  is  soon  overcome 
by  fatigue,  and  to  swim  for  any  length  of  time  he  must  exe- 
cute other  movements  considerably  complicated  in  their 
combinations.  It  is  from  that  modest  amphibian,  the  frog, 
from  which  he  borrows  in  this  case  the  method  of  progres- 
sion, and  this  loan  is  certainly  the  most  inoffensive  of  all 
those  which  he  makes  from  the  animals.  Although  he  seems 
to  turn  his  members  quite  away  from  their  normal  functions, 
he  soon  attains  the  power  of  prolonging  this  exercise,  which 
is  eminently  healthful  and  very  precious,  since  he  finds  in  it  a 
means  of  saving  his  own  life  and  the  lives  of  his  fellowmen. 


CHAPTER    VI. 


The  head.  —  The  skull,  bones  of  the  skull,  sutures,  arch  of  the  skull,  base  of 
the  skull. — Measurement  of  the  skull;  facial  angle,  angle  of  Daubenton; 
comparison  of  the  superficies  of  the  skull  and  of  the  face. — System  of 
Gall.  —  The  face,  boms  of  the  face,  upper  jaw,  loiver  jaw. 


The  Head. — The  head  is  the  most  important  part  of  the 
body,  and  to  it  and  to  the  organs  which  it  contains  our 
attention  is  most  particularly  attracted.  The  heart  and 
lungs  support  life  by  the  respiration  and  the  circulation, 
the  digestive  apparatus  nourishes  the  body,  but  the  head  is 
the  seat  of  intelligence,  the  centre  in  which  all  the  nervous 
impressions  meet  and  from  which  radiates  the  will.  In  the 
head  are  united  the  organs  of  sight,  of  hearing,  of  smell,  and 
of  taste ;  the  face,  almost  entirely  formed  by  the  grouping  of 
these  organs,  expresses  by  the  aid  of  numerous  muscles  the 
impressions  transmitted  to  the  brain,  the  passions,  calmness 
or  agitation  of  mind,  and,  within  certain  limits,  the  phases 
of  thought.  In  other  regions  of  the  body  life  is  unconscious, 
and  the  functions  in  their  performance,  whether  healthy  or 
diseased,  are  executed  mechanically;  the  head  alone  perceives 
sensations  and  interprets  their  meaning,  it  is  by  it  that  man 
knows  himself,  by  it  he  feels  that  he  lives,  and  is  able  to 
say,  "I  think,  therefore  I  am." 

The  head  is  formed  of  two  distinct  parts :  first,  the  skull, 
a  bony  case  which  envelops  the  brain,  and  incloses  in  the 
thickness  of  one  of  the  bones  of  which  it  is  formed  the  organ 
of  hearing;  secondly,  the  face,  in  which  are  united  the 
organs  of  sight,  of  smell,  and  of  taste. 

The  skull  is  composed  of  eight  bones:  the  frontal  or 
coronal,  which  corresponds  to  the  forehead  or  sinciput;  the 


68  THE   HUMAN    BODY. 

occipital  in  the  posterior  part  of  the  skull  or  occiput;  the  two 
parietal  bones,  which  form  the  side  walls  of  the  skull,  and 
contribute,  with  the  frontal  and  occipital,  to  form  its  arch; 
the  two  temporal  bones  occupy,  as  their  name  shows,  the 
region  of  the  temples;  the  ethmoid,  which  owes  its  name  to 
the  sieve-like  plate  of  its  upper  surface ;  and  the  sphenoid,  so 
called  because  it  is  wedged  in  between  all  the  other  bones 
with  which  it  articulates,  and  which  rest  upon  it  as  upon  the 
keystone  of  an  inverted  arch,  thus  forming  the  base  of  the 
skull  on  which  the  brain  rests.  The  frontal,  occipital,  pari- 
etal, and  temporal  bones  are  flat,  formed  of  two  plates  of 
ivory  tissue — internal  and  external  tables — between  which  is 
a  more  or  less  thick  layer  of  spongy  tissue. 

The  bones  of  the  cranium  are  united  by  means  of  sutures 
formed  by  the  junction  of  the  teeth  of  their  serrated  borders, 
almost  precisely  like  what  is  termed  in  architecture  dove- 
tailing. At  birth  the  bones  which  form  the  arch  of  the  skull 
are  united  only  by  a  membranous  tissue,  and  their  borders 
overlap  each  other  even  on  slight  pressure  in  such  a  way  as 
to  lessen  the  diameter  of  the  head ;  but  although  the  sutures 
are  not  yet  developed,  a  part  of  the  tooth-like  processes 
already  exists  in  a  rudimentary  state.  The  membranous 
intervals  are  greater  at  the  point  of  union  of  the  occipital 
and  frontal  with  the  parietal  bones;  these  spaces  are  called 
the  fontanelles.  They  are  soon  filled  with  bony  tissue,  and 
at  four  years  of  age  not  a  trace  of  them  remains.  About 
the  end  of  the  third  year  the  borders  of  the  bones  are  cut 
into  fine  notches  or  teeth,  which  increase  in  number  till  the 
period  of  adolescence.  Before  this  the  suture  which  unites 
the  two  halves  of  the  frontal  bone  begins  to  disappear;  and 
later  still,  when  the  brain  is  fully  developed,  the  other 
bones  gradually  close  together. 

The  internal  surface  of  the  skull  presents  a  series  of 
depressions,  portions  of  the  arch  which  have  been  called 
fossa,  and  according  to  the  bones  which  constitute  them,  the 
frontal,  occipital,  and  temporal  fossce,  and  which  correspond 
to  the  projections  which  we  see  on  the  external  surface. 
There  are  also  a  great  number  of  projections  and  depressions, 
which  to  a  certain  extent  are  modelled  to  the  surface  of  the 


THE    SKULL — THE    FACIAL   ANGLE.  69 

brain,  but  which  form  no  relief  on  the  outside  of  the  skull. 
There  is  no  opening  in  the  arch  of  the  skull,  but  there  are 
several  in  its  base  through  which  the  nerves  and  blood- 
vessels pass;  the  most  important  of  these  is  the  foramen 
magnum,  which  is  the  communication  between  the  cavity  of 
the  skull  and  the  vertebral  canal. 

The  skull  is  oval  in  form  flattened  at  the  base,  with  the 
larger  end  at  the  back.  It  is  never  perfectly  symmetri- 
cal, and  differs  in  shape  and  size  according  to  age,  the  in- 
dividual, and  the  race.  It  is  larger  in  proportion  in  the 
infant  than  in  the  man,  and  in  the  white  race  than  in  the 
other  races.  But  whatever  may  be  the  varieties  which  it 
presents,  they  appear  exclusively  in  the  arch. 

Starting  from  the  principle  that  the  skull  is  modelled  upon 
the  brain,  in  measuring  its  dimensions  we  seek  to  ascertain  that 
of  the  organ  which  it  incloses.  To  attain  this  object,  Camper 
drew  two  straight  lines,  the  one  starting  from  the  first  in- 
cisors of  the  upper  jaw  and  passing  over  the  median  line  of 
the  forehead ;  the  other  starting  from  the  auditory  canal  and 
carried  horizontally  till  it  encountered  the  first,  formed  with 
it  an  angle  called  the  facial  angle,  which  is  from  80  to  85 
degrees  in  the  European,  75  in  the  Mongolian  race,  and  70 
in  the  Negro.  This  anatomical  character,  considered  as  an 
expression  of  intelligence,  did  not  escape  the  notice  of  the 
artists  of  antiquity.  The  statues  which  they  have  bequeathed 
to  us  prove  this ;  among  their  gods,  the  facial  angle  of  Jupiter 
Trophonius,  for  example,  is  90  degrees. 

Daubenton  proposed  to  measure  the  occipital  angle  to  com- 
plete the  measurement  of  Camper,  which  applied  only  to  the 
anterior  portion  of  the  skull;  but  these  angular  measure- 
ments would  not  give  the  extent  of  a  solid  nor  of  a  cavity; 
the  thickness  of  the  bones  at  certain  points,  and  the  varying 
development  of  the  cavities  or  sinuses  comprised  between 
the  internal  and  external  tables,  would  take  from  these 
measurements  much  of  their  signification.  In  order  to  be 
more  exact,  Cuvier,  dividing  the  head  by  a  section  from 
front  to  back,  compared  the  area  of  the  skull  with  that  of  the 
face,  leaving  out  the  lower  jaw:  he  found  that  in  Europeans, 
the  area  of  the  skull  was  four  times  that  of  the  face,  and  in 


70  THE   HUMAN    BODY. 

the  Negro  the  area  of  the  face  is  greater  by  a  fifth,  that  of 
the  skull  being  proportionally  less. 

This  last  method  of  measurement,  even  though  it  gives  an 
idea  of  the  relative  intelligence  within  narrow  limits  only, 
is  at  least  founded  upon  certain  facts,  and  it  expresses  the 
law  of  the  proportional  development  of  the  face  and  skull  in 
the  superior  animals.  And  even  in  measuring  by  the  facial 
angle  the  causes  of  error  may  be  avoided  to  a  certain  extent, 
and  this  measurement  is  an  expression  of  an  incontestable 
anatomical  fact. 

But  this  is  not  the  case  with  a  doctrine  which  was  received 
with  enthusiasm  about  the  beginning  of  this  century,  though 
now  almost  forgotten.  We  speak  of  phrenology.  Gall  pro- 
fessed to  discover  the  degree  of  development  of  the  faculties 
by  exploring  the  cranium.  According  to  his  theory,  the 
skull  is  moulded  upon  the  brain,  and  presents  protuberances 
corresponding  to  those  of  that  organ,  and  thus  gives  the 
measure  of  the  development  of  the  intellectual  and  emotional 
faculties.  These  faculties,  which  he  localized  in  the  ence- 
phalon,  were  composed,  according  to  him,  of  a  series  of 
conoid  bundles,  the  base  of  which  corresponded  to  the  sur- 
face of  the  brain  and  the  apex  to  the  medulla  oblongata. 
Each  one  of  these  cones  was  the  seat  of  a  faculty,  of  which  he 
numbered  twenty-seven,  placing  all  the  intellectual  faculties 
in  the  anterior  portion  of  the  brain,  the  animal  faculties  in 
the  posterior  portion,  and  the  moral  faculties  in  the  middle 
portion  over  the  ear :  the  first  confined  for  the  most  part  to  a 
very  small  space,  and  the  others  distributed  over  larger 
surfaces.  The  pupils  of  Gall  added  eleven  faculties  to  those 
which  he  had  classed.  Among  the  latter,  the  sense  of 
right  and  wrong — or  as  they  termed  it,  conscientiousness — 
did  not  appear. 

To  this  system  it  was  objected  that  if  the  principal  projec- 
tions of  the  exterior  of  the  skull,  the  frontal  and  parietal 
protuberances,  for  example,  correspond  to  the  depressions 
or  fossae  of  the  interior,  no  external  relief  indicated  the 
digital  impressions  and  the  small  cavities  which  correspond 
to  the  surface  of  the  brain ;  that  at  several  points  an  external 
projection  corresponded  to  one  on  the  inner  surface;  that 


THE    SYSTEM    OF   GALL — THE    FACE.  71 

the  arch  of  the  brow  (the  superciliary  ridge),  where  six 
faculties  are  located,  is  more  or  less  prominent,  not  from 
the  cerebral  relief,  but  from  the  development  of  the  frontal 
sinuses;  a,nd  that  there  is  no  resemblance  between  the  form 
of  the  internal  table  and  the  external  table  in  the  frontal 
region.  Gall  was  therefore  wrong  in  tracing  upon  the  brain 
the  seat  of  each  faculty  according  to  the  elevations  which 
he  found  upon  the  skull.  It  was  added  also,  that,  even 
admitting  the  localization  of  the  faculties  and  the  divisions 
of  the  brain,  it  was  very  irrational  to  unite  all  the  faculties 
in  corresponding  portions  of  the  cranial  arch,  and  to  attri- 
bute none  at  all  to  those  portions  of  the  brain  which  are  not 
in  contact  with  the  skull,  or  which  rest  laterally  and  in  front 
on  its  base.  This  exclusive  grouping  was  unjustifiable,  and 
is  to  be  considered  as  purely  arbitrary. 

Gall  and  his  school  invoked  the  aid  of  the  comparative 
anatomy  of  the  brain  in  support  of  his  system.  Leuret  gave 
them  a  death-blow  by  showing  that  the  study  of  the  brain 
in  the  animal  scale  proves  the  facts  to  be  in  entire  disagree- 
ment with  the  theory  of  the  German  savant,  and  that  it  dis- 
proves at  all  points  the  propositions  of  phrenology. 

The  face  is  composed  of  fourteen  bones,  which  form,  by 
their  union  with  each  other  and  with  the  bones  of  the  skull, 
the  cavities  in  which  the  organs  of  sight,  of  smell,  and  of 
taste  are  placed.  Twelve  of  these  bones  are  in  pairs,  and 
placed  symmetrically  on  each  side:  these  are  the  superior 
maxillary,  the  malar  or  cheek  bones,  the  nasal  bones,  the 
lachrymal  bones,  the  superior  turbinated  bones,  and  the 
palatine  bones.  Two  are  not  paired:  these  are  the  vomer 
and  the  inferior  maxillary.  The  superior  maxillaries,  with 
the  lachrymal  and  malar  bones,  combine  to  form  the  inferior 
portion  of  the  orbit;  they  are  united  to  the  temporal  bones 
by  the  malar  bones,  the  protuberances  of  which  form  the 
cheek-bones.  At  their  alveolar  border  the  teeth  are  placed, 
and  the  space  included  in  the  dental  arch  is  called  the  pala- 
tine arch,  which  is  prolonged  backward  by  the  palatine  bones. 
The  nasal  bones  form  the  upper  portion  or  root  of  the  nose ; 
below  these,  and  between  the  superior  maxillaries,  is  the 
nasal  cavity,  which  is  divided  into  two  parts  by  a  partition, 


72  tHE    HUMAN    BODY. 

of  which  the  vomer  forms  a  portion.  The  superior  turbinated 
bones  articulate  with  the  maxillaries  and  contribute  to  mul- 
tiply the  nasal  sinuses,  in  which  are  the  ramifications  of  the 
olfactory  nerves. 

The  inferior  maxillary  is  at  first  composed  of  two  bones, 
which  are  early  joined  together  at  the  point  called  the  sym- 
physis  of  the  chin.  The  branches  of  this  bone  form  a  right 
angle  with  its  body,  called  the  angle  of  the  jaw>  and  at  their 
superior  extremity  they  divide  into  two  apophyses;  namely, 
the  condyle,  which  articulates  with  the  glenoid  cavity  of  the 
temporal  bone,  and  the  coronoid  process,  where  the  tendon 
of  the  temporal  muscle  is  inserted.  This  is  one  of  the 
muscles  which  draw  the  lower  jaw  to  the  upper  one  in  chew- 
ing the  food. 

This  skeleton,  with  its  strange  and  imperfect  outlines,  this 
type  of  Death,  disappears  under  the  muscles  and  teguments, 
which  cover  it  with  an  elegant  envelope.  The  eyelids  veil 
the  orbit  and  protect  the  eye,  the  watchful  sentinel  and  inves- 
tigator of  the  exernal  world,  the  admirable  instrument  which 
enables  the  brain  to  contemplate  the  works  of  creation  and 
to  express  its  most  vivid  impressions.  The  nose  covers  the 
organs  of  smell,  while  it  completes  them  by  protecting  their 
sensibility;  the  lips  are  placed  before  the  mouth,  and  they 
are  at  once  an  organ  of  prehension,  a  docile  and  indefatig- 
able guard,  a  necessary  instrument  in  articulating  sounds, 
and  one  of  the  most  expressive  of  the  features  which  com- 
bine to  form  the  physiognomy.  The  concha,  or  external 
ear,  surrounds  the  auditory  canal,  and  serves  to  collect  the 
sonorous  waves,  and  to  give  expression  to  the  head.  The 
hair,  the  eyebrows,  and  eyelashes  protect  the  skull  and  the 
eye  against  external  objects,  and  at  the  same  time  their  dif- 
ferent shades,  and  curves,  and  undulations,  greatly  contri- 
bute to  the  beauty  of  the  whole.  Lastly,  the  skin  of  the 
face  is  animated  with  the  most  delicate  tints,  or  is  clothed 
in  the  vigorous  tones  and  that  admirable  carnation  which 
has  been  so  well  rendered  by  the  Venetian  painters. 


CHAPTER  VII. 


Digestion. —  Waste  of  the  organism  repaired  by  alimentation. — Hunger. — 
Thirst. — Organs  of  digestion  ;  abdominal  cavity,  peritoneum. — Diges- 
tive apparatus. — Mouth,  lips,  cheeks,  teeth,  palate,  soft  palate,  tongue. — 
Pharynx. — (Esophagus. — Stomach. — Intestinal  canal;  small  intestine, 
large  intestine,  intestinal  convolutions,  mesentery,  omen  turn. — Mucous 
membrane.  —  Liver.  —  Pancreas.  —  Spleen . — Kidneys.  —  Mechanism  of 
digestion. — Digestion  of  the  stomach,  gastric  juice,  peristaltic  movement, 
chyme. — Intestinal  digestion,  bile,  pancreatic  juice,  chyle. — Absorption; 
endosmosis,  exosmosis,  functions  of  the  veins  and  lymphatic  vessels  in 
absorption,  rapidity  of  absorption. 


Digestion. — The  human  body  loses  every  day  through  vari- 
ous channels,  by  exhalation  or  excretion,  about  310  grains 
of  nitrogen,  an  essential  principle  of  animal  matter,  and 
6^2  Ibs.  of  water,  and  burns  io*/2  ounces  of  carbon  in 
contact  with  the  oxygen  of  the  atmosphere.  A  very  short 
time,  therefore,  is  sufficient  to  exhaust  the  organism  if  it  does 
not  find  in  the  alimentation  the  new  elements  by  which  it 
is  reconstructed.  Of  this  unceasing  necessity  of  repairing 
the  loss  which  the  organs  sustain  by  the  action  of  life,  man 
is  imperiously  reminded  by  hunger  and  thirst;  hard  condi- 
tions of  existence.  He  can  support  the  first  of  these  wants  for 
a  time,  which  varies  according  to  age  and  individual  strength; 
it  is  a  sensation  agreeable  at  first,  but  it  soon  becomes  a 
torture,  a  succession  of  atrocious  pains,  and  moral  and  physi- 
cal destruction  follow.  The  annals  of  hunger  are  terrible  in 
science  and  in  history;  it  has  been  called,  with  too  much 
reason,  an  evil  counsellor,  and  he  who  has  the  means  to 
appease  it  each  day  should  be  thereby  reminded  of  those 
less  fortunate  than  himself. 


74 


THE    HUMAN    BODY. 


Thirst  is  a  sensation  painful  from  the  first,  and  can  be 
borne  for  a  shorter  time  than  hunger ;   for  it  necessarily  im- 
plies the  privation  of  all  liquid  aliment,  and  exhaustion  super- 
venes much  sooner  than  when  a 
man  is  deprived  of  solid  food, 
but  is  able  by  the  aid  of  a  little 
water  to  prolong  his  life  for  some 
days. 

The  organs  of  digestion,  of  which 
we  will  give  a  summary  idea,  are, 
for  the  most  part,  contained  in 
the  abdomen. 

Abdominal  cavity. — This  ca- 
vity is  the  largest  in  the  body;  it 
is  situated  below  the  chest,  from 
which  it  is  separated  by  the  dia- 
phragm, and  extends  to  the  lower 
'  extremity  of  the  trunk.  It  is 
divided  into  several  parts  or  re- 
gions, which  are — ist.  In  the 
upper  portion,  the  epigastrium, 
corresponding  to  what  is  called 
the  pit  of  the  stomach,  and  the 
two  hypochonders  (hypo,  under; 
chondros,  cartilage),  which  rise  up 
from  each  side  of  the  epigastrium, 
under  the  double  arch  of  the 

Fig.  si.— Section  of  the  trunk  and  its  diaphragm  and  under  the  car- 
tilages of  the  ribs.  2d.  In  the 
middle,  the  umbilical  region,  and 
the  flanks  or  sides.  3d.  In  the 
lower  portion,  the  hypogastrrum 
or  lower  belly,  and  the  iliac 
fossa,  inclosed  by  the  bones  of  the  same  name.  The  walls 
of  the  abdomen  are  formed  principally  by  muscles  and  apon- 
euroses,  combined  with  the  vertebral  column  and  the  bones 
of  the  pelvis.  The  lower  or  false  ribs  have  only  an  in- 
direct connection  with  the  abdominal  cavity,  resulting  from 
its  being  set  into  the. bottom  of  the  chest 


cavities  in  the  median  line. 

A.  Cavity  of  the  chest. 

B.  Diaphragm. 

C.  Abdominal  cavity. 

D.  Vertebral  column. 

E.  Spinal  canal. 


ABDOMINAL    CAVITY — ORGANS   OF    DIGESTION.  75 

The  abdominal  cavity  is  lined  with  a  serous  membrane 
called  the  peritoneum.  Like  all  the  membranes  of  this 
nature,  it  is  formed  of  cellular  or  laminated  tissue  and 
elastic  fibres;  its  free  surface  is  covered  with  an  epithelium, 
a  sort  of  epidermis,  which  resists  the  continual  friction  result- 
ing from  the  movements  of  the  organs;  and  lastly,  like  all 
its  congeners,  it  is  a  sac  without  an  opening,  folded  on  itself, 
and  consequently  with  double  walls.  The  space  between 
these  walls  is  empty,  their  corresponding  surfaces  rub  freely 
against  each  other,  and  are  moistened  by  a  fluid  analogous 
to  the  serum  of  the  blood,  a  secretion  peculiar  to  these 
membranes,  and  from  which  they  derive  their  name.  The 
internal  wall  of  the  sac  covers  all  the  organs  which  it  con- 
tains, and  the  external  wall  is  attached  throughout  its  whole 
extent  to  the  cavity  which  it  lines.  We  shall,  by-and-by, 
have  occasion  to  return  to  the  disposition  of  the  peritoneum. 

The  digestive  apparatus  is  one  of  the  most  complex  and 
extensive  in  the  organism;  it  is  accessible  to  our  investiga- 
tions in  all  its  parts,  and  we  are  able  to  follow  the  working 
of  the  functions  which  devolve  upon  it.  We  can  observe 
the  metamorphosis  which  the  food  undergoes;  we  can  repro- 
duce in  our  laboratories  a  part  of  these  transformations;  a 
step  farther,  and,  as  Fontenelle  has  said,  we  should  surprise 
nature  in  the  very  act;  but  this  impossible  step  is  the  immense 
distance  which  separates  inert  matter  from  organized  sub- 
stance, physical  and  chemical  phenomena  from  the  vital 
functions. 

The  organs  of  digestion  are  the  mouth,  the  pharynx,  the 
oesophagus,  the  stomach,  the  liver,  and  the  pancreas.  The 
spleen  and  kidneys  are  appendages  of  the  digestive  apparatus, 
but  belong  rather  to  the  circulatory  or  excretory. 

The  mouth  forms  the  entrance  to  the  digestive  apparatus; 
it  contains  the  organ  of  taste,  and  serves  in  eating  and  in 
articulating  sounds.  Bounded  above  by  the  palatine  arch, 
below  by  a  muscular  wall  and  by  the  tongue,  on  the  sides 
and  in  front  by  the  cheeks  and  the  lips,  the  mouth  presents 
in  front  the  opening  of  the  lips,  behind,  the  isthmus  of  the 
throat  by  which  it  communicates  with  the  pharynx  and  over 
which  the  soft  palate  falls. 


76 


THE    HUMAN    BODY. 


The  lips  form  the  anterior  wall  of  the  mouth,  and  are  com- 
posed principally  of  the  orbicular  muscle  of  the  lips,  to  whose 


LLVEILLt    DEL. 


C.    LAPLANTE 


Fig.  22. —  Section  in  the  median  line  through  the  inferior  portion  of  the  nasal 

fossae,  the  mouth,  pharynx,  larynx,  oesophagus,  and  trachea. 

A.  Mouth.  H.  Superior  vocal  chord. 

B.  Soft  palate.  I.  Inferior  vocal  chord. 

C.  Tongue.  K.    Ventricle  of  the  larynx. 

D.  Tonsil.  L.  Larynx. 

E.  Epiglottis.  M.  N.  Trachea  or  windpipe. 

F.  Thyroid  cartilage.  O.  Pharynx,  before  which  is  seen  the 

G.  Arytenoid  cartilage.  cricoid  cartilage. 

concentric  fibres  are  attached  nearly  all  the  muscles  of  the 
face ;  a  very  thick  skin  intimately  united  with  the  orbicular 


THE    LIPS THE    CHEEKS.  77 

muscle,  a  layer  of  small  salivary  glands  subjacent  to  it,  and  the 
mucous  membrane,  complete  these  two  movable,  extensible, 
and  contractile  veils.  The  lips  are  an  organ  of  prehension 
and  suction;  they  prevent,  especially  the  under  lip,  the 
escape  of  saliva;  they  assist  in  the  articulation  of  sounds 
and  in  playing  upon  wind-instruments;  and  lastly,  they  take 
an  extensive  part  in  the  expression  of  the  physiognomy. 
Abundantly  provided  with  nerves  and  vessels,  the  lips  are 
extremely  sensitive,  especially  on  their  borders,  where  the 
skin  grows  thin,  takes  a  carnation  tint,  and  is  insensibly 
transformed  into  mucous  membrane.  Although  the  orbicular 
muscle  limits  them  in  a  measure,  and  imposes  upon  them 
certain  functions  and  a  distinct  region,  they  are  in  reality 
only  the  anterior  portion  of  the  cheeks,  with  which  they  are 
in  constant  communication  by  movement  and  function. 

The  cheeks  form  the  sides  of  the  face  and  the  lateral  walls 
of  the  mouth.  They  embody  in  their  substance  the  muscles 
intrusted  with  the  performance  of  the  complex  functions 
of  the  mouth.  One  of  these  muscles,  peculiar  to  that  part 
of  the  cheek  which  forms  the  buccal  wall,  brings  the  food 
between  the  jaws  and  reacts  against  the  distension  of  the 
cheeks  by  the  air.  Its  action  in  playing  on  wind-instru- 
ments has  given  it  the  name  of  buccinator;  it  contributes 
also  to  the  expression  by  drawing  the  commissure  of  the  lips 
backward,  while  the  great  and  small  zygomatic  muscles  raise 
it.  The  triangular  muscle  of  the  lips,  on  the  contrary,  lets 
it  fall ;  and  lastly,  the  masseter,  a  thick  muscle  of  great  power, 
brings  the  lower  jaw  against  the  upper  one,  and  with  the 
temporal  muscle  performs  mastication.  The  internal  face  of 
the  cheeks  is  covered  with  mucous  membrane,  and  its  whole 
surface  is  scattered  over  with  little  openings,  which  give  pas- 
sage to  the  saliva,  which  is  secreted  by  a  great  number  of 
glandules  analogous  to  those  in  the  lips.  Near  the  middle 
is  the  opening  of  the  canal  of  Stenon,  through  which  the  saliva 
secreted  by  the  parotid  gland  is  poured  into  the  mouth.  This 
gland  is  situated,  as  its  name  indicates,  in  front  of  the  ear, 
and  is  the  most  important  of  the  salivary  glands. 

The  teeth  are  implanted  in  the  alveolar  border  of  the  upper 
and  lower  jaw,  forming  two  symmetrical  arcades,  and  when  the 


78  THE    HUMAN    BODY. 

mouth  is  closed  they  circumscribe  its  limits  like  an  internal 
wall.  They  are  twenty  in  number  in  the  child,  and  thirty-two 
in  the  adult.  They  are  divided  into  eight  incisors,  four  canine, 
and  twenty  molars.  The  last  four  molars  are  called  the 
"wisdom  teeth."  A  tooth  is  composed  of  three  distinct 
parts:  the  pulp,  the  ivory,  and  the  enamel.  Vessels  and 
nerves  penetrate  the  pulp,  but  do  not  go  beyond;  the  ivory 
which  envelopes  the  pulp  constitutes  the  root  and  the  crown 
of  the  teeth.  That  part  of  the  tooth  where  the  crown  joins 
the  root  is  called  the  neck.  This  last  is  covered  with  a  layer 
of  bony  tissue.  The  crown  commences  at  the  neck,  and  is 
overlaid  with  the  enamel,  a  tissue  very  poor  in  animal  sub- 
stances, and  almost  inorganic.  The  teeth  are  not  bones; 
though  their  roots  have  an  osseous  covering,  they  do  not 
present  either  in  their  essential  parts — the  ivory  and  the 
enamel — or  in  their  mode  of  development  and  their  physio- 
logical conditions,  any  connection  with  the  osseous  system; 
they  are  considered  as  analogous  to  the  epidermic  productions, 
the  hair,  nails,  &c.,  which  they  resemble  in  many  respects. 

Palate. — The  palatine  arch  is  formed,  as  we  have  already 
seen,  by  the  upper  jaw-bones  and  the  palatine  bones.  It  is 
circumscribed  in  front  and  on  the  sides  by  the  upper  teeth. 
It  is  covered  with  a  thick  mucous  membrane,  very  hard,  and 
presenting  transverse  ridges.  Behind,  it  is  continued  by  a 
musculo-membranous  partition,  called  the  veil  of  the  palate — 
the  soft  palate — covered  anteriorly  by  the  mucous,  buccal, 
posteriorly  by  the  pituitary  membrane.  Its  inferior  border 
is  free  and  floating,  presenting  on  the  median  line  an  appen- 
dage called  the  uvula.  Each  of  its  lateral  borders  forms 
a  continuation  with  the  tongue  and  the  pharynx  by  two 
folds,  which  are  called  the  pillars  of  the  soft  palate,  and  be- 
tween which  on  either  side  lie  the  tonsils.  In  a  state  of 
repose  the  soft  palate  closes  the  back  part  of  the  mouth; 
but  when  raised  prevents  the  food  and  drink,  and  the  voice 
also,  from  passing  into  the  nasal  fossae. 

The  tongue  is  a  fleshy  body,  symmetrical,  longer  than  it  is 
broad,  flattened  from  above  downwards,  thicker  toward  the 
middle  than  at  its  extremities,  larger  behind  than  in  front, 
and  rounded  on  the  edges.  The  posterior  extremity  of  the 


THE    TONGUE.  79 

tongue  is  called  its  root,  and  the  anterior  the  point  or  tip. 
Its  upper  surface  or  back,  and  a  part  of  its  edges,  are  covered 
over  with  papilla,  which  are  divided  into  conical,  fungiform, 
and  cup-shaped  papillae.  Its  lower  surface  is  free  for  about 
one-third  of  its  length  anteriorly :  at  the  point  of  attachment 
we  observe  a  mucous  fold  called  the  frcenum  lingua  or  bridle 
of  the  tongue.  Its  two  posterior  thirds  receive  the  muscles 
which  fasten  it  to  the  neighbouring  parts.  The  base  or  root 
of  the  tongue  is  fixed  to  the  hyoid  bone,  an  osseous  semi- 
circle bifurcated  at  its  extremities,  placed  between  the  tongue 
and  the  larynx,  and  bound  to  these  two  organs  by  muscles, 
which  gives  unity  to  their  movements  in  rising  and  falling. 
The  tongue  is  formed  of  muscles,  some  of  which  are  proper 
to  itself,  and  others  attach  it  to  the  hyoid  bone,  to  the  lower 
jaw,  and  to  the  styloid  process  of  the  temporal  bone.  All 
these  muscles  interlace  their  fibres  in  an  inextricable  manner, 
especially  towards  the  upper  portion  of  the  tongue.  At  the 
median  line  and  in  the  centre  they  are  fixed  to  a  cartila- 
ginous plate,  a  sort  of  indirect  prolongation  of  the  hyoid 
bone,  which  gives  greater  solidity  to  the  whole.  The  buccal 
mucous  membrane  covers  the  tongue,  and  is  remarkably 
dense  on  its  dorsal  face. 

The  complex  interlacement  of  the  muscular  fibres  of  the 
tongue  permits  a  great  variety  of  motion.  It  can  raise  or 
lower  itself,  lengthen  or  shorten,  shrink  or  expand,  diminish 
the  end  to  a  point,  bend  itself  upwards  and  downwards,  hollow 
itself  into  a  canal  lengthwise  or  breadthwise,  carry  its  point 
and  its  edges  to  the  parts  of  the  mouth  into  which  mastica- 
tion has  dispersed  the  food ;  in  short,  it  exhibits  in  its  move- 
ments and  changes  of  form  great  force  and  the  most  subtle 
dexterity. 

The  tongue  receives  three  nerves;  the  great  hypoglossal, 
the  lingual,  and  glosso-pharyngeal ;  the  first  gives  motion,  and 
the  last  two  are  the  sensitive  nerves  of  taste.  Under  the 
influence  of  the  first  it  takes  part  in  the  functions  of  diges- 
tion and  in  the  articulation  of  sounds,  and  endowed  by  the 
others  with  a  special  sensibility,  it  is  the  principal  organ 
of  taste. 

The  bottom  of  the  buccal  cavity  communicates  with  the 


80  THE    HUMAN    BODY. 

pharynx,  a  canal  with  elastic  walls  formed  by  muscles,  and 
lined  with  mucous  membrane.  It  extends  from  the  back  of 
the  mouth  to  the  oesophagus,  and  is  the  vestibule  of  this 
passage,  a  sort  of  funnel,  the  upper  part  of  which  shares  in 
deglutition,  and  adds  to  the  resonance  of  the  voice.  The 
anterior  wall  of  the  oesophagus  is  formed  by  the  larynx,  the 
superior  orifice  of  which,  surmounted  by  the  epiglottis,  opens 
into  the  pharyngeal  cavity,  so  that  it  is  only  the  half  of  a 
canal  completed  in  front  by  the  larynx. 

The  pharynx  is  continued  below  by  the  oesophagus,  a  tube 
formed  by  two  membranes,  the  external  muscular  and  the 
internal  mucous.  It  is  extensible  and  very  contractile;  it 
descends  between  the  spinal  column  and  the  trachea,  which 
it  overlaps  a  little  to  the  left,  and  on  reaching  the  thorax  it 
follows  the  posterior  mediastinum,  and  at  last  traverses  the 
diaphragm  and  opens  into  the  stomach. 

The  stomach. — The  form  of  the  stomach  has  been  com- 
pared to  that  of  a  bagpipe.  It  is  a  large  pouch,  an  expan- 
sion of  the  digestive  tube,  placed  transversely  across  the 
upper  portion  of  the  abdomen.  Its  left  extremity  or  great 
cul-de-sac,  lying  in  the  hypochondriac  region,  is  rounded  and 
larger  than  the  right,  which  corresponds  to  the  epigastrium. 
Above,  it  forms  a  concave  curve — the  lesser  curvature;  be- 
low, a  convex  curve — the  greater  curvature.  The  opening  by 
which  it  communicates  with  the  oesophagus  is  to  the  right 
of  the  great  cul-de-sac,  and  is  called  the  cardiac  orifice; 
and  that  which  opens  into  the  intestine,  the  pylorus,  or  pyloric 
orifice. 

The  walls  of  the  stomach  are  formed  of  four  membranes, 
which,  proceeding  from  without  inwards,  are  a  serous — the 
peritoneum — a  muscular,  a  fibrous,  and  a  mucous  membrane. 
The  muscular  membrane  is  composed  of  three  layers  of 
fibres,  some  longitudinal,  others  circular.  These  fibres  are 
slender  and  open  for  the  most  part,  but  near  the  pylorus 
they  are  closer  and  stronger,  and  around  this  orifice  they 
form  a  muscular  ring,  which  has  been  named  the  pyloric 
valve. 

The  intestinal  canal  is  a  continuation  of  the  stomach;  its 
walls,  like  those  of  that  organ,  are  composed  of  four  mem- 


THE    INTESTINAL   CANAL. 


8l 


branes — a  serous,  muscular,  fibrous,  and  mucous  membrane. 
It  is  divided  into  the  large  and  small  intestines.  The 
smaller  intestine  is  composed  of  the  duodenum,  jejunum, 
and  ileum.  The  duodenum  is  so  named  because  it  measures 


Fig.  23. — Transverse  section  of  the  thoracic  and  abdominal  cavities. 


A.  Heart 

B.  Lungs  separated  to  show  the  heart. 

C.  Diaphragm. 

D.  Liver. 


E.  Gall-bladder. 

F.  Stomach. 

G.  Small  intestine. 
H.  Transverse  colon. 


nearly  twelve  finger-breadths  in  length;  it  extends  from  the 
stomach  to  the  jejunum,  from  which  no  line  of  demarcation 
separates  it,  nor  is  the  jejunum  separated  from  the  ileum. 
These  names  indicate  a  purely  arbitrary  distinction,  drawn 
by  the  ancient  anatomists  between  these  three  parts  of  the 
intestinal  canal.  The  large  intestine  differs  from  the  small 
one  externally  in  size,  and  because  it  presents  a  series  of  more 

6 


82  THE    HUMAN    BODY. 

marked  enlargements.  The  coscum  is  its  upper  portion,  of  a, 
larger  calibre  than  the  ileum,  and  separated  from  it  by  the 
ileo-c&cal  valve,  a  fold  of  the  internal  membranes  designed  to 
prevent  the  reflux  of  fluids.  It  opens  into  the  ileum,  not  at 
its  extremity,  but  by  a  lateral  orifice;  below  this  orifice,  it 
forms  a  sort  of  ampulla,  terminated  by  the  appendix  vermi- 
formis.  The  ccecum  is  followed  by  the  colon,  from  which  it 
is  separated  only  by  an  artificial  division.  It  is  the  largest 
and  longest  portion  of  the  large  intestine;  it  forms  a  curve 
called  the  arch  of  the  colon,  and  is  divided  into  the  ascending, 
transverse,  and  descending  colon,  to  which  succeeds  the  rectum, 
the  extremity  of  the  intestinal  canal. 

The  total  length  of  the  intestine  is  about  nine  yards.  It 
occupies  a  large  portion  of  the  abdomen,  in  which  it  is  folded 
in  numerous  convolutions. 

The  peritoneum  (peri,  around;  teinein,  to  stretch)  enve- 
lops the  intestinal  canal,  attaches  it  to  the  vertebral  column 
by  a  double  membranous  fold,  called  the  mesentery,  and  par- 
tially covers  it  by  a  floating  fold  or  epiploon.  Imagine  a 
membrane  doubled  back  so  as  to  form  a  long  broad  fold. 
At  the  bottom  of  and  within  this  fold  lies  the  intestine,  which 
we  may  suppose  to  be  stretched  in  a  straight  line.  The 
membrane  adheres  closely  to  three-quarters  of  the  surface 
of  the  intestine,  and  then  folds  back  on  itself.  The  two 
leaves  of  this  peritoneal  covering  are  united  by  cellular 
tissue,  which  permits  their  separation  by  distension  of  the 
intestines.  If  now  we  pucker  the  fold  at  its  root,  the 
border  which  contains  the  intestine  will  form  numerous 
sinuosities,  and  this  is  really  the  arrangement  of  the  intes- 
tinal convolutions.  In  the  region  of  the  colon,  the  fold 
formed  by  the  peritoneum  is  very  much  broader,  the  in- 
testine lies  in  the  middle  of  its  breadth,  and  the  rest  falls 
like  a  veil  in  front  of  the  intestinal  mass,  and  rises  to  the 
stomach,  which  it  partially  covers  as  well  as  the  liver  and 
spleen.  This  moving  veil  is  the  epiploon  (epi,  upon;  pleo,  I 
float).  That  part  of  the  fold  behind  the  intestine  fastens  it- 
self to  the  front  of  the  vertebral  column,  and  takes  the  name 
of  mesentery  (niesos,  middle,  and  mteron,  intestine). 

The  mucous  membrane. — This  membrane  is  to  the  cavities 


MUCOUS   MEMBRANE — LIVER.  83 

which  it  lines,  what  the  skin  is  to  the  surface  of  the  body. 
It  is  an  internal  skin,  which  is  a  continuation  of  the  external. 
Like  the  skin,  it  is  an  organ  of  absorption  and  secretion. 
It  is  composed  of  a  corium  or  true  skin  and  a  sort  of  epi- 
dermis, named  the  epithelium,  variable  in  its  texture  and  in 
its  elements  according  as  it  is  to  offer  more  or  less  resistance. 
A  peculiar  fluid — mucus — is  secreted  by  this  membrane  and 
preserves  its  softness.  The  mucous  membrane  is  covered, 
throughout  the  digestive  canal,  even  to  the  end  of  the  small 
intestine,  with  great  numbers  of  papillae  or  villi,  and  espe- 
cially on  the  tongue.  In  the  stomach  it  has  numerous  folds, 
which  are  effaced  when  the  organ  is  distended;  and  through- 
out the  smaller  intestine  it  forms  the  valvitla  conniventes, 
wrinkles  or  folds  designed  to  increase  the  extent  of  absorbing 
surface. 

The  liver  is  an  organ  of  a  glandular  nature,  arid,  like  all 
the  glands,  is  designed  to  secrete  a  peculiar  fluid.  It 
separates  from  the  blood  the  elements  which  constitute  bile. 
Situated  in  the  right  hypochonder,  it  enters  the  arch  of  the 
diaphragm ;  and  it  occupies  also  a  portion  of  the  epigastrium, 
and  then  comes  in  contact  with  the  stomach,  the  arch  of  the 
colon,  &c. ;  behind,  it  corresponds  to  the  vertebral  column, 
the  aorta,  and  the  descending  vena  cava ;  in  front  to  the  base 
of  the  chest.  It  is  held  in  its  place  by  ligamentous  folds  of 
the  peritoneum;  the  most  important  of  these  is  the  suspen- 
sory ligament.  The  form  of  the  liver  is  difficult  to  describe : 
its  upper  surface  is  convex,  its  lower  slightly  concave.  It  is 
divided  into  the  right  and  left  lobes;  to  the  latter  is  attached 
an  appendage  named  lobus  Spigelii  or  Spigel's  lobe.  The 
under  surface  of  the  liver  is  marked  by  the  longitudinal  and 
transverse  fissures.  Through  this  last  the  portal  vein  enters. 
Examined  en  masse,  the  liver  is  of  a  reddish-brown  colour. 
Its  substance  is  yellowish,  granular,  and  contained  in  an 
envelope  of  cellular  tissue  called  Glissorfs  capsule.  Several 
kinds  of  vessels  are  found  in  it:  the  hepatic  artery,  which 
carries  the  blood  which  nourishes  the  organ;  the  portal  vein, 
which  carries  the  blood  to  the  liver  which  is  to  be  purified; 
the  hepatic  vein,  which  transmits  to  the  descending  vena  cava 
the  blood  elaborated  by  the  gland;  and  lastly,  the  bile-ducts^ 


84  THE    HUMAN    BODY. 

which  secrete  or  transport  the  fluids  extracted  from  the  blood 
by  the  liver  to  the  gall-bladder,  situated  under  the  right  lobe. 

The  tissue  proper  of  the  liver  is  essentially  constituted  by 
the  secretory  canals  of  the  bile,  each  one  of  which  ter- 
minates in  an  acinus  or  lobule ;  a  net-work  of  capillaries  of 
the  portal  vein  surrounds  these  lobules,  which  by  their  union 
in  clusters  form  the  liver,  and  which  are  so  many  diminu- 
tives of  that  gland.  The  secretory  ducts  are  continuous 
with  the  hepatic  ducts,  and  the  capillaries  of  the  portal  vein 
with  those  of  the  hepatic  veins,  which  transmit  to  the  inferior 
vena  cava  the  blood  from  which  the  bile  has  been  separated. 
The  liver  secretes  sugar  also,  which,  formed  in  this  gland  at 
the  expense  of  the  blood  from  the  portal  vein,  is  immediately 
decomposed,  and  in  health  disappears  in  the  process  of 
nutrition. 

Pancreas. — This  is  an  elongated  gland  situated  behind  the 
stomach :  it  secretes  the  pancreatic  juice — a  fluid  analogous 
to  the  saliva,  and  which  the  pancreatic  canal  pours  into  the 
ductus  choledochus,  near  its  orifice  in  the  duodenum. 

Spleen. — This  is  a  spongy  vascular  body  situated  in  the 
left  hypochonder,  between  the  stomach  and  the  false  ribs: 
it  serves  as  a  reservoir  in  over-fulness  of  the  portal  vein.  Its 
special  use  and  purpose  are  unknown. 

The  kidneys  are  two  in  number,  and  are  placed  on  the 
right  and  left  of  the  lumbar  vertebrae  in  the  lowest  part  of 
the  hypochonders.  They  are  glands  of  a  peculiar  and  very 
complicated  structure.  They  separate  the  urea  from  the 
blood,  and  transmit  to  the  bladder  the  urinary  secretion  by 
two  canals  called  ureters.  The  upper  portion  of  the  kidneys 
is  covered  by  the  supra-renal  capsules,  the  use  of  which  is 
not  known. 

Mechanism  of  digestion. — This  function  consists  in  the 
decomposition,  liquefaction,  and  absorption  of  alimentary 
substances;  it  prepares  the  nutriment  by  separating  the 
assimilable  portions  which  are  to  be  mingled  with  the  blood 
from  those  which  are  not  fit  to  enter  into  the  organism. 
The  aliments  undergo  in  the  mouth  the  first  change  neces- 
sary to  their  introduction  into  the  digestive  canal,  which  is 
also  no  less  important  in  relation  to  their  chemical  trans- 


DIGESTION    IN    THE    STOMACH    AND    INTESTINES.  85 

formation.  They  are  here  mixed  with  the  saliva,  which 
penetrates  them  thoroughly,  softens  and  dissolves  them  in 
part,  and  thus  renders  their  mastication,  taste,  and  degluti- 
tion more  easy.  The  saliva  also  transforms  the  amylaceous 
substances  contained  in  the  food  first  into  dextrine  and  then 
into  glycose  or  sugar;  it  reduces  a  portion  of  the  fatty 
bodies  to  an  emulsion — that  is  to  say,  it  separates  them  into 
particles  held  in  suspension  in  the  salivary  fluid,  and  begins 
the  decomposition  which  is  completed  in  the  digestive  canal. 

Digestion  in  the  stomach. — From  the  mouth  the  alimentary 
mass  descends  through  the  pharynx  and  oesophagus  to  the 
stomach,  where  it  mingles  with  the  gastric  juice,  one  of  the 
most  powerful  agents  of  digestion.  The  gastric  juice  is 
secreted  by  glandular  tubes  situated  in  the  mucous  mem- 
brane of  the  stomach.  It  is  a  colourless  fluid,  saltish  as  well 
as  acid  to  the  taste.  It  contains,  among  other  elements, 
alkaline  chlorides,  lactic  acid,  and  an  organic  substance 
called  pepsine,  which  is  peculiar  to  it.  The  gastric  juice 
pours  into  the  stomach  in  considerable  quantities  when  food 
is  introduced  into  it,  mingles  there  with  the  mass,  softens  it, 
and  induces  a  fermentation  which  results  in  their  ultimate 
liquefaction.  During  digestion  a  characteristic  movement 
takes  place  in  the  stomach  and  intestinal  canal — the  circular 
fibres  of  the  muscular  membrane  contract  successively  from 
above  downwards,  and  push  the  alimentary  substances  in  the 
same  direction.  Gradually  as  the  lower  fibres  contract  the 
upper  ones  relax  in  order  to  contract  anew.  This  is  called 
the  peristaltic  movement.  Under  its  influence  the  contents  of 
the  stomach  are  kept  incessantly  in  motion,  mixed  with  the 
gastric  juice,  and  directed  toward  \htpylorus.  This  orifice 
is  so  named  because  it  is  like  a  door-keeper  to  the  stomach, 
allowing  the  aliments  which  have  been  sufficiently  elaborated 
to  pass  out  while  the  others  are  retained  in  the  organ. 
After  a  time,  which  varies  from  three  to  five  hours  in  dif- 
ferent individuals  and  at  different  ages,  the  alimentary  mass 
is  converted  into  a  grayish  paste,  acid,  and  almost  fluid;  it 
then  takes  the  name  of  chyme,  and  the  function  of  the 
stomach,  chymification,  is  accomplished. 

Intestinal  digestion. — In  proportion  as  the  chyme  reaches 


86  THE    HUMAN    BODY. 

the  duodenum  through  the  pyloric  orifice,  the  bile  and  the 
pancreatic  juice  mingle  with  it,  as  the  gastric  juice  does  in 
the  stomach.  They  both  aid  in  liquefying  the  chyme  by  the 
water  which  they  contain,  and  by  their  special  action  upon 
the  substances  of  which  it  is  composed:  the  pancreatic  juice 
continues  with  even  more  activity  than  the  saliva  to  trans- 
form the  amylaceous  matter  into  glycose.  The  bile  assists 
the  digestion  of  the  animal  matter  by  reducing  the  fatty 
bodies  to  an  emulsion,  and  it  appears  also  to  act  as  an 
excitant  to  the  function  of  the  intestine;  and  lastly,  a  fluid 
secreted  by  the  mucous  membrane  of  the  intestine,  as  the 
gastric  juice  is  by  the  stomach,  co-operates  with  the  biliary 
and  pancreatic  secretions.  Under  the  influence  of  these 
agents,  of  the  fermentation  induced  by  the  pepsine  and  of 
the  peristaltic  movement,  the  chyme  is  liquefied  during  its 
advance  through  the  smaller  intestine,  and  is  transformed 
into  a  white  milky  fluid — the  chyle — which  the  chyliferous 
vessels  draw  from  the  surface  of  the  mucous  membrane,  and 
carry  to  the  thoracic  duct,  from  whence  it  goes  to  be  mixed 
with  the  blood. 

Absorption. — The  moment  chyle  is  formed  .digestion  proper 
may  be  considered  as  accomplished,  though  on  this  function 
also  depends  the  absorption  of  the  chyle,  which  must  still  be 
perfected  in  its  course  through  the  smaller  intestine  and  the 
veins  before  it  mingles  with  the  blood. 

The  mechanism  of  absorption  is  still  unknown.  It  has  been 
explained  as  taking  place  by  endosmosis — a  phenomenon  dis- 
covered by  Dutrochet,  which  results  from  the  property  which 
tissues  possess,  under  certain  conditions,  of  permitting  fluid 
or  gaseous  bodies  to  pass  through  their  capillary  canals.  If, 
for  example,  two  fluids  which  may  be  mixed,  though  they 
may  be  of  different  natures  and  different  densities,  are  separ- 
ated by  a  membrane,  two  currents  are  established  through 
this  membrane  in  opposite  directions,  and  of  unequal  force, 
tending  to  mix  the  two  fluids,  the  stronger  current  is  gener- 
ally produced  by  the  fluid  the  least  dense;  and  this  is  called 
endosmosis — the  feebler  current  exosmosis.  In  this  experi- 
ment the  substances  mingle  without  changing  their  nature; 
but  it  is  not  so  in  absorption.  The  substances  absorbed  by 


ABSORPTION.  87 

the  organic  tissues  change  incessantly  during  their  progress, 
borrowing  or  lending  elements  to  each  one  of  the  molecules 
through  which  they  pass.  And  farther,  the  different  tissues 
absorb  more  or  less  of  the  same  substance  by  virtue  of  pro- 
perties which  are  unknown.  In  this  way  a  poison  which 
remains  inert  on  the  mucous  membrane  of  the  stomach  is 
rapidly  absorbed  by  the  lungs. 

The  mucous  membranes  absorb  more  rapidly  than  the 
skin,  and  this  tissue  is  more  or  less  permeable  according  to 
its  thickness,  its  density,  as  the  epidermis  which  covers  it  is 
thick  or  thin.  Absorption  is  therefore  very  rapid  in  inocula- 
tion— that  is,  when  the  substance  to  be  absorbed  is  intro- 
duced into  the  substance  of  the  tissues.  Wherever  the  point 
of  absorption  may  be,  it  takes  place  by  the  lymphatic  vessels, 
and  especially  by  the  veins.  The  veins  absorb  a  greater 
number  of  substances  than  the  lymphatics,  and  carry  them 
more  quickly  into  the  circulation;  they  charge  themselves 
especially  with  the  materials  which  are  to  be  rejected  from 
the  economy,  while  the  lymphatics  absorb  from  preference 
those  that  can  still  be  assimilated.  The  veins  and  the 
chyliferous  vessels,  which  are  a  variety  of  the  lymphatics, 
draw  from  the  mucous  membrane  of  the  intestine  the  useful 
products  of  digestion ;  but  the  lymphatics  take  possession  of 
fats,  while  the  veins  prefer  fluids,  albumen,  sugar,  and  salts. 

It  is  well  known  with  what  rapidity  certain  substances 
taken  into  the  alimentary  canal,  or  into  the  lungs,  pass  into 
the  other  organs,  and  exhale,  or  are  eliminated.  Thus  the 
presence  of  the  ferro-cyanide  of  potassium  has  been  recog- 
nized in  the  urine  within  one  minute  after  its  ingestion  into 
the  stomach.  Indigo,  gallic  acid,  and  other  colouring 
matters,  or  those  possessing  a  characteristic  odour,  pass  in 
the  course  of  fifteen  or  twenty  minutes  through  all  the  wind- 
ings of  the  circulation. 

As  has  already  been  stated,  absorption  takes  place  much 
more  rapidly  by  the  skin  when  it  has  been  deprived  of  its 
epidermis.  Five  or  six  minutes  are  generally  a  sufficient  time 
for  the  alkaloids  of  opium  or  belladonna  to  manifest  their 
action  on  the  nervous  system,  and  in  some  cases  this  action 
is  produced  in  a  few  seconds.  Other  substances,  especially 


88  THE    HUMAN    BODY. 

sulphate  of  copper,  are  almost  as  rapid  in  their  effect  on  the 
stomach  as  chloroform  and  several  gases  when  placed  in 
contact  with  the  mucous  membrane  of  the  lungs;  they  pro- 
duce phenomena  which  develop  themselves  with  terrible 
rapidity.  Medicine  derives  great  assistance  from  this  ab- 
sorbent property  of  the  tissues;  thanks  to  which,  humanity 
is  daily  spared  a  vast  amount  of  suffering. 


CHAPTER  VIII. 


Respiration.  —  Thoracic  cavity;  pleura. — Organs  of  respiration:  lungs, 
trachea,  bronchia. — Respiration;  influence  of  respiration  on  the  blood, 
Lavoisier^-  theory,  theory  of  catalytic  phenomena;  mechanism  of  respira- 
tion, respiratory  sounds,  frequency  of  respiration;  capacity  of  the  lungs; 
modification  of  t/ie  air  in  the  lungs.  — Influence  of  atmospheric  pressure 
on  respiration;  mountain-sickness. 


Thoracic  cavity . — The  thorax  or  chest,  as  we  have  already 
seen,  is  formed  by  the  vertebral  column,  the  ribs,  and  the 
sternum.  The  shoulder-blades  and  collar-bones  belong  to 
the  arm,  which  is  an  appendix  of  the  thorax.  The  thorax 
resembles  a  bony  cage  (fig.  1 1,  p.  27),  the  interstices  of  which 
are  filled  with  the  muscles;  the  interior  of  this  cage  is  the 
thoracic  cavity  (fig.  21,  p.  74).  It  is  the  second  cavity  in 
point  of  size  in  the  body;  it  has  the  form  of  a  cone,  slightly 
flattened  from  before  backwards,  with  the  base  turned  down- 
ward, and  hollowed  out  in  front.  It  is  bounded  at  its  apex 
by  the  sternum,  the  clavicles,  the  first  rib  on  the  right  and 
left,  and  the  seventh  cervical  vertebra;  at  its  circumference 
by  the  sternum,  the  ribs,  and  the  dorsal  vertebrae;  at  its  base 
by  the  false  ribs,  the  costal  cartilages,  and  the  xyphoid  car- 
tilage. The  diaphragm  corresponds  to  this  base  (fig.  21, 
p.  74);  this  is  a  muscular  partition,  the  fibres  of  which  radiate 
from  a  central  aponeurosis ;  it  closes  the  chest  at  the  bottom, 
into  which  it  rises  like  an  arch,  a  little  depressed  in  the 
centre.  The  diaphragm  is  attached  to  the  cartilaginous 
border  of  the  false  ribs,  to  the  xyphoid  process,  and  to  the 
lumbar  vertebrae.  This  last  attachment  is  effected  by  mus- 
cular fasciculi,  which  are  called  the  pillars  of  the  diaphragm. 
The  central  aponeurosis  of  this  muscle  is  in  the  form  of  a 


90  THE    HUMAN    BODY. 

clover  leaf;  it  was  considered  a  nervous  centre  by  the 
ancients,  perhaps  because  of  the  pain  and  the  peculiar  sen- 
sations induced  in  the  epigastrium  by  strong  emotions,  or 
because  they  confounded  the  tendinous  fibres  with  the 
nervous  tissue. 

Pleura. — The  cavity  of  the  chest  is  lined  with  a  serous 
membrane,  called  the  pleura,  which  forms  in  each  half  of 
this  cavity  a  sac  without  an  opening.  There  are  therefore 
two  pleurae,  a  right  and  a  left.  Proceeding  from  the  edges 
of  the  sternum  and  the  costal  cartilages,  the  pleurae  cover  the 
lateral  walls  of  the  chest  and  a  portion  of  the  body  of  the 
vertebrae.  They  then  approach  each  other,  leaving  a  space 
between  them  called  fas  posterior  mediastinum.  On  reaching 
the  root  of  the  lungs,  they  turn  from  within  outward,  covering 
a  portion  of  the  pericardium  and  of  the  internal  surface  of  the 
lungs,  their  posterior  borders  and  external  surface ;  they  then 
penetrate  the  interlobular  fissures,  and  fold  back  upon  the 
anterior  border  of  the  lungs  and  upon  their  internal  surface 
quite  to  their  roots;  then  turning  again  forward,  they  cover 
the  sides  of  the  pericardium,  in  front  of  which  they  turn  back 
to  back,  and  then  separating  anew,  they  reach  the  borders 
of  the  sternum  from  whence  they  sprang.  The  space  left 
between  the  pleurae  behind  the  sternum  is  the  anterior  medi- 
astinum, separated,  as  is  seen,  from  the  posterior  mediastinum 
by  the  heart  and  the  root  of  the  lungs.  At  the  top  of  the  chest 
the  pleurae  form  a  conical  cavity,  which  receives  the  apex  of 
the  lung;  at  the  bottom  they  cover  the  superior  surface  of  the 
diaphragm.  In  the  posterior  mediastinum  are  the  oesophagus, 
the  aorta,  the  azygos  vein,  the  thoracic  duct,  and  the  lower 
portion  of  the  trachea.  In  the  anterior  mediastinum  are  the 
pericardium — the  envelope  of  the  heart — and  the  thymus 
gland,  an  organ  whose  uses  are  unknown.  That  part  of  the 
pleurae  which  envelops  the  organs  of  the  chest,  and  that 
which  lines  the  walls  of  this  cavity,  are  thus  in  contact  with 
each  other  without  adhering,  in  a  normal  condition,  and  they 
allow  the  expansion  and  contraction  of  the  lungs  and  the 
walls  of  the  chest.  The  serous  nature  of  the  pleurae  insures 
freedom  of  movement,  and  prevents  all  roughness  in  the 
constant  friction  of  the  surfaces. 


LUNGS. 


91 


Organs  of  respiration.  Lungs. — As  their  name  indicates 
(pneumon,  from  pneo,  I  breathe),  the  lungs  are  the  essential 
organs  of  respiration.  They  are  two  in  number,  though  they 


Fig.  24. — Lungs  and  heart. 


A.  Lungs  ivith   the  anterior  edges 

turned  back  to  show  the  heart 
and  bronchia. 

B.  Heart. 

C.  Aorta. 

D.  Pulmonary  artery. 

E.  Ascending  vena  cava. 

F.  Trachea. 


G,  G.  Bronchia. 

H,  H.  Carotid  arteries. 

I,  I.  Jugular  veins. 

J,  J.  Subclavian  arteries. 

K,  K.  Subclavian  veins. 

P,  P.  Costal  cartilages. 

Q .  An tcrior  ca rdiac  a rtery. 

R.  RigJit  auricle. 


receive  the  air  by  one  canal  and  the  blood  by  a  single  vessel ; 
they  maybe  considered  as  the  terminal  expansion  of  the  rami- 
fications of  the  trachea,  or  as  the  two  heads  of  a  single  tree. 
Placed  in  the  chest,  of  which  they  occupy  the  larger  part, 


92  .  THE    HUMAN    BODY. 

and  to  the  shape  of  which  they  are  moulded  (fig.  23,  p.  81), 
they  represent  two  irregular  cones,  resting  their  bases  on  the 
diaphragm,  filling  with  their  apices  the  two  conical  spaces 
lined  by  the  pleura  at  the  top  of  the  chest,  and  separated  by 
the  heart  and  the  mediastinum.  The  right  lung  is  divided 
in  its  length  into  three  lobes  by  two  oblique  clefts,  and  is 
shorter  and  larger  than  the  left,  which  has  but  two  lobes. 
The  internal  face  of  the  lungs  is  concave;  about  the  middle 
the  bronchia  unite  with  the  pulmonary  vessels  to  form  the 
root  of  the  lungs ;  their  base  takes  the  form  of  the  convexity 
of  the  diaphragm;  their  edges,  thin  in  front  and  at  the  bottom, 
thick  and  rounded  behind,  partially  cover  the  heart,  and  fill 
the  space  which  separates  the  diaphragm  from  the  walls  of 
the  thorax,  as  well  as  the  groove  between  the  ribs  and  the 
vertebrae.  The  entire  surface  of  the  lungs  is  smooth  and 
moistened  with  serous  secretion. 

The  tissue  proper  of  the  lungs,  or  pulmonary  parenchyma, 
is  of  a  grayish  rose  colour,  soft,  spongy,  elastic,  crepitating 
under  pressure  in  consequence  of  the  air  it  contains.  It  is 
divided  into  polyhedral  lobules,  very  variable  in  form  and  in 
the  disposition  of  their  facets,  which  permit  exact  juxtaposi- 
tion without  intervals;  and  they  are  separated  by  partitions  of 
cellular  tissue,  independent  and  without  communication  with 
each  other.  Each  one  of  these  lobules  is  formed  of  a  cluster 
of  little  cavities  called  pulmonary  vesicles,  constituting  a  cul- 
de-sac,  and  receiving  the  air  from  the  bronchial  ramifications 
of  which  they  are  the  terminal  expansions.  The  diameter  of 
these  pulmonary  vesicles  is  from  one-seventieth  to  one  hun- 
dred and  fiftieth  of  an  inch;  from  this  we  can  judge  of  the 
tenuity  of  their  walls,  in  the  substance  of  which  notwithstand- 
ing ramify  the  capillary  vessels.  Each  lobule  represents  a  little 
lung,  a  diminutive  of  the  entire  organ.  A  bronchial  twig  and 
minute  artery  run  into  it,  veins  and  lymphatic  vessels  leave  it. 
On  the  surface  the  lobules  appear  bounded  by  their  interme- 
diate partitions,  and  they  form  a  mosaic  of  which  the  mottled 
colouring  varies  from  rose  to  black.  These  black  particles 
are  principally  composed  of  a  carboniferous  substance  which 
penetrates  the  lung  either  with  the  air  or  with  the  blood,  and 
which  is  called  pulmonary  carbon. 


LARYNX TRACHEA. 


93 


The  lungs  are  supplied  with  air  through  the  larynx,  trachea, 
and  bronchia.  The  larynx,  the  organ  of  the  voice,  of  which 
we  shall  speak  later,  is  continuous  below  with  the  trachea. 
This  is  a  cylindrical  tube  flattened  behind;  it  is  composed 
of  a  series  of  cartilaginous  rings  united  by  a  fibrous  membrane, 


Fig.  25. — Section  showing  the  ramifications  of  the  bronchi  in  the  lungs. 
A.   Trachea.         B,  C.  Bronchi.         D,  D.  Bronchial  tubes. 

and  lined  with  a  mucous  membrane;  it  is  placed  in  the  an- 
terior portion  of  the  neck,  and  passes  vertically  from  above 
downward.  The  rings  of  the  trachea  do  not  extend  quite 
round  it;  interrupted  in  their  circuit  towards  the  posterior 
fourth  of  the  tube,  they  are,  properly  speaking,  only  segments 
of  a  circle.  They  number  from  sixteen  to  twenty,  and  pro- 
duce a  corresponding  number  of  protuberances  on  the  surface 
of  the  trachea,  which  is  thereby  rendered  rough  and  wavy  to 
the  touch.  It  is  from  this  circumstance  that  it  derives  its 


94  THE    HUMAN    BODY. 

name  (trachys,  rough).  Formerly  it  was  confounded  with 
the  arterial  vessels,  which  were  supposed  also  to  be  designed 
to  contain  air. 

At  the  height  of  the  third  dorsal  vertebra,  the  trachea 
divides  into  two  portions,  which  are  called  bronchi,  which 
on  reaching  the  root  of  the  lungs  divide  into  numerous  rami- 
fications designated  bronchia  or  bronchial  tubes,  and  be- 
coming more  and  more  slender.  Of  the  two  principal 
bronchi,  the  right  is  larger  than  the  left,  and  the  left  is  twice 
the  length  of  the  right.  They  are  both,  as  well  as  their  rami- 
fications, up  to  a  certain  limit,  composed  of  fibrous  membrane 
and  incomplete  cartilaginous  rings.  When  their  diameter  has 
decreased  to  less  than  one-fiftieth  of  an  inch,  they  no  longer 
have  the  cartilaginous  rings,  and  the  mucous  membrane 
cannot  be  separated  from  their  walls.  They  continue  to 
subdivide,  and  terminate,  as  already  stated,  in  the  pulmonary 
vesicles,  the  agglomeration  of  which  in  clusters  forms  the 
lobules  of  the  lung. 

Independently  of  the  artery  and  pulmonary  veins  by  which 
the  venous  blood  reaches  the  lung,  and,  transformed  into 
arterial  blood,  is  returned  to  the  heart — that  is,  besides  those 
which  serve  for  the  sanguification  and  circulation — the 
bronchial  veins  and  arteries  carry  the  blood  through  the 
lungs  which  is  destined  to  nourish  the  organ  itself,  and  it  is 
probable  that  the  tissue  proper  of  the  lung  uses  for  itself  part 
of  the  red  blood  formed  in  its  cavities.  Numerous  lymphatic 
vessels  are  also  found  in  the  lungs.  The  nerves  which  are 
distributed  through  the  lungs  come  from  the  pneumogastric 
and  the  ganglion ic  nervous  system. 

Respiration. — Respiration  is  a  function  by  which  the 
oxygen  of  the  air  is  introduced  into  the  blood,  and  by  which 
part  of  the  useless  and  hurtful  materials  are  expelled,  in  a 
gaseous  form,  from  the  organism.  It  is  divided  into  two 
parts :  inspiration,  during  which  the  atmospheric  air  penetrates 
the  pulmonary  cells;  and  expiration,  which  expels  the  air 
which  has  been  changed  during  its  stay  in  the  lungs.  On 
reaching  the  cells  of  the  lungs,  the  blood  is  separated  from 
the  air  by  their  walls  and  those  of  the  capillaries,  which 
ramify  over  them.  However  thin  these  membranes  may  be, 


RESPIRATION.  95 

they  suffice  to  confine  the  air  and  the  blood  in  distinct 
cavities;  but  like  the  other  organic  tissues,  they  have  the 
property  of  allowing  themselves  to  be  penetrated  by  endos- 
mosis  and  exosmosis.  The  oxygen  of  the  air  therefore  passes 
through  them  in  order  to  combine  with  the  blood;  while  those 
gases  contained  in  this  fluid,  which  should  be  eliminated, 
separate  from  it  and  mingle  with  the  air,  which  carries  them 
away  with  it  during  expiration.  It  is  an  interchange  of  gases 
between  the  air  and  the  blood,  the  air  giving  up  oxygen 
to  the  blood,  and  receiving  from  it  other  gaseous  fluids, 
among  which  carbonic  acid  gas  predominates  in  volume. 
This  being  in  excess  in  the  venous  blood  is  exhaled  from 
the  lungs,  while  the  oxygen  of  the  air  combines  with  the 
blood  which  is  carried  to  the  heart  by  the  veins,  which  has 
been  deprived  of  a  part  of  its  nutritive  elements,  and  has 
become  unfit  to  support  life.  On  coming  in  contact  with 
the  oxygen,  the  venous  blood  loses  its  dark  colour,  becomes 
a  brilliant  red,  and  returns  to  the  heart  transformed  into  arte- 
rial blood.  This  group  of  phenomena  is  called  sanguifi- 
cation. 

On  the  one  hand  the  oxygen  of  the  atmosphere  burns 
carbon  in  the  lung,  on  the  other  the  lung  exhales  carbonic  acid 
gas,  nitrogen,  and  the  vapour  of  water.  From  whence  are 
these  gases  and  this  water  derived?  The  carbonic  acid  gas 
is  not  produced  in  the  lungs  alone.  The  venous  blood 
reaches  the  organ  of  respiration  poor  in  oxygen,  and  charged 
relatively  with  the  carbonic  acid  gas  which  it  has  received  in 
its  course  from  all  the  tissues ;  everywhere  this  acid  has  been 
produced  by  the  combination  of  the  carbon  with  the  oxygen, 
which  in  the  lung  is  borrowed  from  the  air,  but  everywhere 
else  it  comes  from  the  arterial  blood.  In  a  word,  the  oxygen 
combined  with  the  blood  by  respiration,  is  separated  from  it 
little  by  little  in  the  capillaries  throughout  the  whole  body  in 
order  to  produce  numerous  products,  among  others  car- 
bonic  acid  gas.  On  leaving  the  heart  and  in  the  arteries, 
the  blood  contains  24  parts  of  oxygen  per  1000,  in  the  veins 
it  contains  only  n  per  1000.  As  for  the  nitrogen  and  the 
vapour  of  water,  one  is  disengaged,  and  the  other  produced 
during  this  same  process  of  nutrition,  and  both  are  drawn 


96  THE    HUMAN    BODY. 

from  the  principles  in  the  organism  which  are  introduced  into 
it  by  digestion  or  respiration. 

Lavoisier  was  the  first  to  demonstrate  the  absorption  of 
oxygen  by  respiration,  and  to  show  by  experiment  the  analogy 
existing  between  combustion  and  respiration.  "  Respiration," 
said  he,  "  is  nothing  but  a  slow  combustion  of  carbon  and 
hydrogen,  which  resembles,  iri  every  respect,  that  which  takes 
place  in  a  lamp.  ...  In  respiration,  as  in  combustion,  it 
is  the  atmosphere  that  furnishes  the  oxygen.  .  .  .  But  since, 
in  respiration,  it  is  the  substance  of  the  animal  itself,  it  is 
the  blood  which  furnishes  the  combustible,  if  animals  do 
not  regularly  repair  by  alimentation  that  which  they  lose  by 
respiration  the  oil  in  the  lamp  will  soon  be  wanting,  and  the 
animal  will  perish  as  the  lamp  will  go  out  for  the  want  of 
nourishment."  Most  physiologists  have  admitted  Lavoisier's 
theory,  and  they  consider  respiration  a  slow  combustion  of 
the  materials  of  the  blood  by  the  oxygen  of  the  atmosphere, 
and  as  the  source  of  animal  heat.  We  have  just  seen  that  this 
combustion  takes  place,  not  only  in  the  lungs,  but  through- 
out the  whole  extent  of  the  organs  where  the  arterial  blood 
carries  the  oxygen  which  presides  over  the  phenomena  of 
nutrition,  that  is,  over  the  assimilation  of  the  elements  of 
which  the  blood  is  formed,  and  over  the  decomposition  of 
some  of  these  principles  of  which  certain  parts  only  remain 
in  the  system,  while  others  return  to  be  burned  in  the 
capillaries  of  the  lungs,  or  to  be  exhaled  in  the  form  of  gas 
or  vapour  of  water. 

Some  authors  again  do  not  admit  that  combustion  takes 
place  in  respiration,  the  phenomena  of  which,  of  quite  a  dif- 
ferent order  according  to  them,  may  be  attributed  to  a  reac- 
tion induced  by  the  contact  of  organized  substances.  The 
decomposition  and  disassimilation  of  these  are  due  to  a  series 
of  acts  of  which  very  little  is  known,  and  which  are  compared 
to  what  has  been  termed  by  Berzelius  u  catalytic  phenomena" 
But  we  confine  ourselves  to  a  mention  only  of  this  doctrine, 
which  is  not  generally  accepted. 

Mechanism  of  respiration. — We  have  seen  that  respiration 
is  divided  into  two  movements — inspiration  and  expiration. 
In  inspiration,  the  diaphragm  contracts  and  sinks  down,  push- 


MECHANISM    OF    RESPIRATION.  97 

ing  the  abdominal  organs  downward.  The  ribs  rise  by  the 
contraction  of  numerous  muscles ;  at  the  same  time  with  the 
sternum,  which  is  carried  forward,  the  intercostal  spaces  en- 
large, and  the  chest  is  developed  in  all  its  dimensions,  verti- 
cally, antero-posteriorly,  and  transversely.  In  expiration,  the 
inspiratory  muscles  relax,  and  others,  especially  those  of  the 
abdomen,  lower  the  ribs  and  the  sternum  by  contracting  the 
chest;  while  the  lungs,  distended  by  the  air  inspired,  collapse 
under  the  pressure  of  the  thoracic  walls  and  their  own  proper 
elasticity.  The  experiments  of  Duchenne  of  Boulogne  tend 
to  prove  that  this  contraction  of  the  lungs  is  due  to  the 
muscular  fibres  which  accompany  the  bronchia  down  to  their 
minutest  ramifications. 

Nearly  all  the  inspirations  are  effected  by  the  movements 
of  the  diaphragm  and  the  inferior  ribs  only.  From  time  to 
time  a  deeper  and  more  complete  inspiration  causes  the 
thorax  to  rise,  not  simultaneously  but  successively  at  the  base, 
then  at  the  apex.  In  the  first  case  the  respiration  is  dia- 
phragmatic; when  the  lower  and  middle  ribs  are  raised  it  is 
termed  lateral;  and  lastly,  when  the  first  rib  and  clavicle  take 
part  in  the  movement,  it  is  costo-superior  or  clavicular.  In 
diaphragmatic  respiration,  as  M.  Mandl  has  observed,  the 
larynx  is  immovable,  the  inspiration  is  easy,  without  effort, 
and  permits  exertion  in  singing  or  in  gymnastics  for  a  long 
time  and  without  fatigue.  On  the  contrary,  persons  who 
respire  principally  by  the  upper  ribs  are  easily  fatigued,  and 
very  soon  out  of  breath.  This  is  seen  in  women  when  the 
corset  compresses  the  base  of  the  chest,  and  in  singers  who 
adopt,  on  erroneous  principles,  the  bad  habit  of  clavicular 
respiration.  In  this  last  method  of  inspiration  the  larynx  is 
drawn  down  by  the  contraction  of  the  external  muscles,  and 
its  action  becomes  painful.  The  effort  of  the  inspiratory 
muscles  rapidly  induces  fatigue,  and  the  inspiration,  always 
incomplete,  becomes  also  more  frequent.  Diaphragmatic 
respiration  is  practised  by  mountaineers,  gymnasts,  and  skilful 
singers — a  habit  induced  either  by  instinct,  or  a  well-directed 
education. 

The  respiratory  movements  are  not  completely  under  the 
control  of  the  will.  It  is  not  possible  long  to  suppress  the 

7 


98  THE    HUMAN    BODY. 

contrary  movement  after  an  inspiration,  and  when  expiration 
has  taken  place  the  need  of  inspiration  soon  makes  itself  im- 
periously felt.  It  is  impossible,  in  fact,  to  retain  the  breath 
except  for  a  very  short  space  of  time,  two  or  three  minutes 
at  the  longest:  the  most  thoroughly  trained  divers  not  being 
able  to  exceed  this  limit. 

Respiratory  sounds.  —  In  a  normal  condition,  and  when 
awake,  respiration  takes  place  without  noise  when  the  move- 
ment is  moderate;  but  when  inspiration  and  expiration  are 
strong  and  deep,  it  is  accompanied  by  a  noise  caused  by  the 
air  passing  through  the  nasal  passages  or  the  mouth.  During 
sleep  the  column  of  air  breaks  against  the  soft  palate  and 
produces  snoring.  Besides  these  sounds,  which  are  exterior 
to  the  chest,  there  are  others  produced  by  the  passage  of 
the  air  through  the  bronchial  tubes;  and  when  the  ear  is 
applied  to  the  chest  of  a  person  in  good  health,  a  soft  and 
regular  murmur  is  heard  in  rhythm  with  the  respiration;  this 
is  called  the  vesicular  murmur.  Several  morbid  causes 
change  the  nature  of  this  murmur,  suppress  it,  or  produce 
others.  These  are  so  many  signs  which  enable  the  physician 
to  determine  the  condition  of  the  respiratory  organs. 

Frequency  of  respiration. — In  an  adult  in  a  condition  of 
repose,  respiration  takes  place  about  eighteen  times  a  minute, 
in  the  infant  it  is  more  frequent.  As  is  well  known,  it  be- 
comes very  active  under  the  influence  of  bodily  exertion,  or 
under  excitement  from  any  cause  whether  physical  or  moral. 
When,  on  the  other  hand,  the  attention  is  fixed  on  a  laborious 
effort,  the  breath  is  held  so  that  it  very  soon  becomes 
necessary  to  take  long  and  deep  inspirations  to  compensate 
for  the  insufficiency  of  those  which  preceded.  This  result 
of  hard  work  or  great  strain  of  mind  should  be  guarded 
against  in  children,  as  their  constitution  suffers  greatly  under 
the  influence  of  incomplete  respiration. 

Capacity  of  the  lungs. — It  is  estimated  that  the  lungs  of  a 
man  from  thirty-five  to  forty  years  old  will  contain  about 
225  cubic  inches  of  air;  it  is  less  before  that  age,  and  falls  to 
a  little  less  than  200  cubic  inches  at  sixty  years  of  age.  The 
capacity  is  smaller  in  women,  and  varies  also  according  to 
the  individual.  It  is  only  possible  to  obtain  approximate 


CHANGES    ON    THE    AIR    IN    THE    LUNGS.  99 

experimental  results,  as  the  lungs  are  not  completely  emptied 
at  each  expiration,  and  the  cells  always  retain  a  quantity  of 
air,  and  this  quantity  is  greater  in  proportion  as  the  respiration 
is  calm  and  shallow. 

Changes  on  the  air  in  the  lungs. — It  is  clear  from  the  fore- 
going, that  the  air  which  is  expired  has  neither  the  same 
volume  nor  the  same  proportion  of  constituent  elements  as 
the  air  which  is  inspired.  In  fact,  an  adult  man  absorbs  by 
respiration  from  450  to  550  grains  of  oxygen  in  an  hour. 
He  exhales  in  the  same  time  632  grains  of  carbonic  acid;  a 
less  quantity  of  nitrogen,  amounting  to  about  a  hundredth  of 
the  oxygen  absorbed;  and  lastly,  about  9720  grains  of  water 
in  the  form  of  vapour.  This  exhalation  of  water  by  the  lungs 
constitutes  the  pulmonary  perspiration,  a  function  analogous 
to  the  perspiration  of  the  skin.  The  expired  air,  as  already 
stated,  is  deprived  of  a  portion  of  its  oxygen,  and  is  charged 
with  carbonic  acid  gas.  The  proportion  of  this  gas  is  about 
4  parts  in  100.  From  350  to  400  cubic  feet  of  air  are  taken 
into  the  lungs  in  24  hours,  and  rapidly  changed,  and  the 
gravest  consequences  result  from  placing  a  man  under  condi- 
tions in  which  the  air  cannot  be  renewed.  During  the  Eng- 
lish war  in  India  in  the  last  century,  one  hundred  and  forty- 
six  prisoners  were  shut  up  in  a  room  scarcely  large  enough  to 
hold  them,  into  which  the  air  could  only  enter  by  two  narrow 
windows;  and  at  the  end  of  eight  hours  only  twenty-three 
remained  alive,  and  these  were  in  a  most  deplorable  condi- 
tion. Percy  relates  that  after  the  battle  of  Austerlitz,  three 
hundred  Russian  prisoners  were  confined  in  a  cavern,  and 
two  hundred  and  sixty  of  these  unfortunates  perished  in  a 
few  hours  from  asphyxia. 

Influence  of  the  pressure  of  the  atmosphere  on  respiration. 
Mountain-sickness. — It  is  well  known  that  the  density  of  the 
air  diminishes  with  the  atmospheric  pressure,  that  is,  in  the 
lower  regions  of  the  air,  on  the  sea-coast  for  example,  the 
air  is  denser  than  in  elevated  regions.  Thus  in  order  to 
absorb  the  quantity  of  oxygen  necessary  for  sanguification,  it 
is  necessary  to  respire  oftener  upon  high  mountains  than 
when  on  plains,  but  this  acceleration  of  respiration  is 
perceptible  only  when  the  height  is  considerable  and  the 


100  THE    HUMAN    BODY. 

distance  rapidly  passed  over.  Gay-Lussac,  who  in  his 
balloon  ascension  rose  to  a  height  of  22,956  feet  in  six 
hours,  found  his  respiration  disturbed,  and  greatly  accelerated; 
and  having  made  no  movement  requiring  exertion,  he  could 
only  attribute  this  condition  to  the  diminution  of  the  pressure 
of  the  atmosphere.  But  in  climbing  mountains  the  move- 
ment and  efforts  of  walking  are  added  to  the  influence  of  the 
height;  and  when  the  difference  in  altitude  in  one  day 
amounts  to  6560  feet,  a  notable  acceleration  of  respiration 
and  quickening  of  the  pulse  is  observed,  which  in  many 
instances  is  accompanied  by  a  peculiar  sense  of  uneasiness, 
which  has  been  termed  mountain-sickness.  The  most  remark- 
able symptoms  are  fatigue  or  rather  partial  paralysis  of  the 
muscular  system,  and  especially  of  the  muscles  of  locomotion. 
This  paralysis  of  the  legs  increases  with  every  step  until, 
having  gone  a  certain  distance  with  increasing  difficulty,  it  is 
impossible  to  take  another  step.  A  rest  of  a  few  seconds  is 
sufficient  for  the  muscles  to  regain  their  power,  and  it  seems 
as  if  the  traveller  could  go  on  without  fear  of  a  recurrence  of 
the  difficulty;  but  very  soon  it  returns,  and  a  fresh  halt  is 
necessary.  The  higher  one  goes  the  shorter  the  distance 
that  can  be  passed  without  resting — from  one  hundred  and 
fifty  steps  the  distance  falls-off  to  one  hundred — to  fifty — and 
at  last  to  twenty  or  thirty.  Inclination  to  sleep,  oppression 
of  the  heart,  and  loss  of  spirit  are  sometimes  added  to  this 
periodic  exhaustion  of  strength,  and  in  some  persons  mountain- 
sickness  is  closely  analogous  to  sea-sickness.  In  others  the 
symptoms  are  such  as  are  always  induced  in  the  respiration, 
circulation,  and  in  consequence  in  the  muscular  system,  by 
violent  exercise.  Thirty  steps  in  climbing  a  high  mountain 
cause  as  much  fatigue  as  a  forced  march  or  run  on  a  plain. 
Respiration,  quickened  by  motion  and  disturbed  by  succes- 
sive efforts,  is  no  longer  sufficient  for  sanguification;  the  pro- 
portion between  the  venous  and  the  arterial  blood  is  no 
longer  normal;  and,  above  all,  sanguineous  congestion,  which 
is  inseparable  from  violent  exertion,  takes  place  in  the  lungs, 
in  the  brain,  and  other  organs.  But  as  soon  as  the  muscles 
have  relaxed  for  a  few  moments,  two  or  three  full  in- 
spirations rapidly  relieve  the  congestion,  while  a  flood  of 


MOUNTAIN -SICKNESS.  IOI 

arterial  blood  proceeds  from  the  heart  to  revive  the  whole 
organism. 

Up  to  a  height  of  16,400  feet,  man  can  easily  acclima- 
tize himself  to  the  rarefied  air.  Baron  Humboldt  saw  Peru- 
vians cultivating  the  land  at  Antisana,  situated  13,454  feet 
above  the  level  of  the  sea;  and  agricultural  labour  requires 
the  development  of  an  amount  of  force  incompatible  with 
mountain-sickness,  even  though  an  energy  like  that  of  our 
European  cultivators  may  not  be  found.  Jacquemont  visited 
villages  in  Thibet  at  a  height  of  16,400  feet.  La  Paz  is 
situated  on  the  Andes  at  a  height  of  12,195  feet,  but  the 
inhabitants  suffer  no  inconvenience  from  the  rarity  of  the 
atmosphere;  though  strangers  can  walk  only  a  short  distance 
without  stopping,  and  they  are  specially  uncomfortable  if  the 
young  Peruvian  ladies  mischievously  invite  them  to  a  few 
turns  in  a  waltz.  It  is  hardly  necessary  to  remark  that  these 
symptoms  are  not  equally  urgent  in  all  those  who  expose 
themselves  to  this  rarefied  air.  Some  individuals  scarcely 
feel  them,  and  are  soon  acclimatized,  while  others  suffer 
greatly  for  a  long  period.  A  host  of  circumstances  and 
special  conditions  contribute  also  to  render  these  symptoms 
more  or  less  marked,  and  mountaineers  themselves  some- 
times experience  them  as  well  as  the  inhabitants  of  less  ele- 
vated countries. 


CHAPTER  IX. 


Circulation. — Organs  of  the  circulation;  heart,  pericardium;  arteries, 
capillaries,  principal  arteries;  veins,  principal  veins ;  portal  system; 
lymphatic  vessels  and  ganglia. — Mechanism  of  the  circulation;  dis- 
coz'ery  of  the  circulation,  action  and  sounds  of  the  heart,  arterial  circu- 
lation, pulse,  capillary  circulation;  venous  circulation,  valves  of  the 
veins;  discharge  of  chyle  and  lymph  into  the  veins.  Sanguification; 
circulation  in  the  pulmonary  artery,  capillaries,  and  pulmonary  veins. 
— Influences  which  accelerate  or  retard  the  beating  of  the  heart. 


Circulation. — The  blood  is  carried  by  the  arteries  from  the 
heart  to  all  the  organs,  and  it  returns  by  the  veins  from  all 
the  organs  to  the  heart.  This  movement  of  the  blood  to  and 
from  every  portion  of  tire  body,  from  the  heart  as  the  point 
of  departure,  is  called  the  circulation.  The  transportation  of 
chyle  and  lymph  by  the  lymphatic  vessels,  which  are  the 
tributaries  and  purveyors  of  the  sanguiferous  system,  is  con- 
nected also  with  the  circulation. 

Organs  of  the  circulation. — The  heart  is  a  hollow  muscular 
organ,  nearly  in  the  form  of  a  cone,  of  which  the  base  is 
equal  to  the  height,  and  about  the  size  of  the  fist  in  the 
adult.  It  is  situated  towards  the  middle  of  the  chest,  a  little 
to  the  left  (fig.  24,  p.  91),  and  between  the  pleurae,  which 
contribute  to  form  its  covering.  Its  apex  is  directed  down- 
ward, forward,  and  towards  the  left,  at  about  the  level  of  the 
fifth  rib;  its  base  looks  upward,  and  slightly  backward,  and 
is  protected  by  the  sternum.  Its  anterior  face,  turned 
upward  and  to  the  right,  is  marked  by  a  longitudinal  furrow, 
as  is  also  its  posterior  face,  which  is  turned  downward  and  to 
the  left.  Internally  the  heart  is  divided  by  a  muscular  par- 
tition into  two  nearly  equal  halves,  placed  back  to  back,  and 


THE  HEART. 


103 


these  are  each  again  divided  laterally  into  two  cavities,  the 
superior  called  the  auricle,  and  the  inferior  the  ventricle.  The 
auricles  take  their  name  from  a  flattened  appendage  which 


Fig.  26. — Heart  and  principal  arterial  and  venous  trunks. 


A.  Rigiit  ventr'cle. 

B.  Left  ventricle. 

C.  RigJit  auricle. 

D.  Left  auricle. 

E.  Aorta. 

F.  Pulmonary  artery. 


G.   Brachio-cephalic  trunk. 
H.   Carotid,  right  and  left. 
I,  I.  Subclavian  arteries. 
K.  Superior  vena  cava. 
L.  Pulmonary  veifis. 


falls  down  upon  their  external  face.  The  right  auricle  com- 
municates with  the  right  ventricle,  and  the  left  auricle  with  the 
left  ventricle.  There  is  no  communication  between  the  ven- 
tricles, but  before  birth  the  two  auricles  communicate  by  an 
orifice,  which  is  obliterated  during  the  first  months  of  life, 


104  THE    HUMAN    BODY. 

leaving  as  the  only  trace  of  its  existence  a  depression  called 
the  fossa  ovalis. 

The  superior  and  inferior  vena  cava  open  into  the  right 
auricle,  and  at  the  orifice  of  the  latter  is  the  Eustachian 
valve.  The  orifices  of  the  right  and  left  pulmonary  veins 
are  in  the  left  auricle. 

The  opening  by  which  the  auricles  and  ventricles  commu- 
nicate with  each  other  is  called  the  auriculo-ventricular 
opening.  These  orifices  are  furnished  with  valves;  that  on 
the  right  is  called  the  tricuspid  valve,  from  the  three  angles 
which  are  formed  by  its  leaves;  and  that  on  the  left  is  called 
the  mitral  valve,  from  the  slight  resemblance  which  it  bears  to 
a  bishop's  mitre. 

The  cavities  of  the  heart  are  lined  by  the  endocardium,  a 
very  fine,  smooth  membrane,  which  has  been  compared  to 
the  serous  membranes.  These  cavities  present  numerous 
inequalities,  which  result  from  the  projection  of  the  bundles 
of  muscular  fibre  which  point  in  every  direction.  In  the  ven- 
tricles these  fascicles  form  fleshy  columns  (columna  camece), 
disposed  in  a  net-work  running  from  one  point  of  the  walls  to 
another,  and  several  which  take  part  in  the  movement  of 
the  valves,  send  out  to  these  valves  a  crowd  of  little  tendons. 
The  walls  of  the  left  ventricle  are  much  thicker  and  more 
resistant  than  those  of  the  right  ventricle. 

Pericardium. — This  is  the  term  applied  to  the  covering 
which  envelops  the  heart;  it  is  a  sac  composed  of  two  layers, 
a  fibrous  membrane  on  the  outside,  and  a  serous  membrane 
on  the  inside.  This  last  covers  the  external  surface  of  the 
heart,  and  is  reflected  back  upon  itself  in  order  to  form,  like 
all  the  membranes  of  this  nature,  a  sac  without  an  opening. 
The  heart  is  thus  covered  by  the  pericardial  sac,  but  not 
contained  inside  its  cavity.  A  correct  idea  may  be  formed 
of  the  disposition  of  the  pericardium  around  the  heart  by 
recalling  a  very  common  and  very  convenient,  though  now 
discarded  head-dress,  the  cotton  night-cap.  The  pericardium 
incloses  the  heart  exactly  as  this  cap  covered  our  forefathers' 
heads. 

Arteries. — The  vessels  which  carry  the  blood  from  the 
right  ventricle  to  the  lungs,  and  from  the  left  ventricle  to  the 


ARTERIES. 


whole  system,  are  called  arteries.  The  first-named,  the  rami- 
fications of  the  pulmonary  artery,  contain  the  dark  blood 
which  is  carried  to  the  lungs  to  be  oxygenized  by  contact 
with  the  air.  It  is  on  the  contrary  red  blood  which  runs  in 
the  aorta,  the  original  trunk  of  all  the  arteries  distributed 


A-1 


Fig.  27. -Transverse  section  of  the  heart. 


A.  Right  ventricle. 

B.  Left  ventricle. 
C    Right  auricle. 

D.  Left  auricle. 

E.  Right  auricula-ventricular  orifice 

and  tricuspid  valve. 

F.  Left  auriculo-ventriciilar   orifice 

and  mitral  valve. 


G.   Origin  of  tJie  pulmonary  artery 

and  sigmoid  valves. 
H.    Origin  of  tJie  aorta,  and  valves. 
I.  Orifice  of  inferior  vena  cava. 
K.  Superior  vena  cava. 
L,  L.   Orifice  of  the  pulmonary  veins. 


through  the  body.  There  are  two  classes  of  arteries,  one 
pertaining  to  the  pulmonary  system  or  lesser  circulation,  and 
the  other  to  the  aortic  or  general  circulation.  We  will  first 
consider  the  last-named. 

The  ancient  anatomists,  finding  the  arteries  empty  after 
death,  believed  that  they  were  designed  to  contain  air,  and 
from  this  circumstance  they  derive  their  name  (aer,  air,  and 


106  THE    HUMAN    BODY. 

terein,  to  contain).  For  the  same  reason,  and  with  more 
accuracy,  they  named  the  tube  which  conveys  the  air  to  the 
lungs  the  trachea-artery. 

Galen  discovered  the  presence  of  blood  in  the  arteries, 
but  he  retained  the  name,  and  others  have  continued  it, 
although  it  does  not  accord  with  their  functions. 

The  walls  of  the  arteries  are  composed  of  three  superposed 
coats.  The  outer  one  is  nbro-cellular,  vascular,  and  very 
resistant;  the  middle  one,  the  membrane  proper  or  elastic, 
is  less  resistant,  and  changes  its  texture  under  the  influence 
of  age  or  other  causes.  The  inner  is  extremely  thin,  and  is 
analogous  in  texture  to  the  endocardium.  When  a  ligature 
is  applied  to  an  artery,  the  internal  and  middle  coats  are 
broken  through  by  the  pressure,  but  the  external  one 
resists  it. 

The  arteries  communicate  with  each  other  in  their  course 
through  the  body,  and  especially  toward  the  extremities  by 
numerous  anastomoses — that, is,  they  join  each  other  either 
by  means  of  branches,  or  by  forming  a  net-work,  the  meshes 
of  which,  rounded  and  in  arches,  are  closer  in  proportion 
as  the  twigs  are  smaller.  They  terminate  in  innumerable 
microscopic  ramifications,  called  the  capillary  vessels,  which 
are  intermediate  between  the  ends  of  the  arteries  and  the 
veins. 

The  walls  of  the  arteries  are  nourished,  like  all  other  parts 
of  the  body,  by  the  vasa  vasorum,  or  vessels  of  the  vessels. 
And  lastly,  the  arteries  are  enveloped  in  their  course  by 
numerous  nervous  filaments  from  the  great  sympathetic 
nerve,  and  by  lymphatic  vessels. 

The  arteries  which  penetrate  the  substance  of  muscles, 
like  those  of  the  thigh  and  leg,  are  protected  by  an  aponeu- 
rotic  sheath,  and  by  fibrous  rings  which  prevent  them  from 
being  pulled  out  of  place  or  compressed  during  the  contrac- 
tion of  the  muscles  which  surround  them. 

Principal  arteries. — The  aorta,  which  is  the  main  trunk  of 
the  arterial  system  which  carries  the  red  blood,  is  the  largest 
artery  in  the  system.  It  commences  at  the  upper  portion  of 
the  left  ventricle,  not  far  from  the  ventriculo-aortic  orifice; 
it  has  three  valves,  called  the  sigmoid  or  semi-lunar  valves, 


PRINCIPAL   ARTERIES.  107 

which  serve  to  prevent  the  reflux  of  the  blood,  and  which 
completely  close  the  vessel  when  expanded. 

The  aorta  runs  upward  and  to  the  right,  and  is  here  the 
ascending  aorta;  then  it  turns  to  the  left,  passing  in  front  of 
the  spinal  column,  and  taking  a  new  turn  downward,  it  forms 
the  arch  of  the  aorta;  it  runs  along  and  to  the  left  of  the 
spine  through  the  posterior  mediastinum,  and  is  called  the 
descending  aorta,  and  passes  through  the  opening  in  the  dia- 
phragm. On  reaching  the  abdomen  it  becomes  the  abdo- 
minal aorta,  up  to  about  the  fourth  lumbar  vertebrae,  where 
it  bifurcates  and  forms  the  two  primitive  iliac  arteries. 

From  its  upper  portion  the  aorta  throws  off  important 
branches,  of  which  the  principal  are  the  following: — The 
brachio-cephalic  or  innominate  artery,  which  springs  from  the 
arch,  and  is  its  representative  on  the  right  side  of  the  chest. 
This  trunk  gives  off  the  right  common  carotid  and  subdavian; 
the  left  common  carotid  and  subdavian  spring  directly  from 
the  arch  of  the  aorta. 

The  common  carotid  arteries  run  upward  along  the  outside 
of  the  neck  on  a  level  with  the  upper  border  of  the  thyroid 
cartilage,  and  each  divides  into  the  external  and  internal 
carotid. 

The  external  carotid  gives  off  the  superior  thyroid,  the 
facial,  lingual,  and  occipital  arteries.  At  the  level  of  the  con- 
dyle  of  the  jaw  it  divides  into  the  temporal  and  internal 
maxillary. 

The  internal  carotid  runs  upward  along  the  cervical  ver- 
tebrae, enters  the  skull,  gives  off  the  ophthalmic  artery,  and  is 
distributed  through  the  brain. 

The  subdavian  runs  outside,  behind  and  below  the  clavicle, 
as  its  name  indicates,  and  gives  off,  among  other  branches,  the 
vertebral  artery,  and  the  internal  mammary;  and  on  reaching 
the  arm-pit  (axilla)  it  takes  the  name  of  the  axillary  artery, 
and  gives  off  important  vessels  to  the  shoulder  and  chest; 
and  then  descending  along  the  humerus  under  the  name  of 
the  brachial  artery,  it  divides  below  the  elbow,  and  forms  the 
radial  and  ulnar  arteries,  which  furnish  the  vessels  of  the 
fore-arm  and  those  of  the  hand. 

Among  the  arteries  arising  from  the  descending  aorta  we 


108  THE    HUMAN    BODY. 

will  mention  only  the  coeliac  trunk,  which  divides  into  three 
branches,  destined  to  the  liver,  the  stomach,  and  the  spleen; 
the  superior  and  inferior  mesenteric,  which  go  to  the  mesentery 
and  intestines;  and  the  renal  or  emulgent  arteries. 

Iliac  arteries. — The  common  iliac  arteries,  formed  by  the 
bifurcation  of  the  aorta,  run  obliquely  downward  to  the 
right  and  left.  After  attaining  a  length  of  about  two  and  a 
half  inches,  each  one  divides  into  the  internal  iliac,  which 
ramifies  on  the  inside  and  on  the  outside  of  the  pelvic 
cavity,  and  the  external  iliac,  which  at  the  point  where  it 
leaves  the  pelvis  gives  off  the  epigastric  artery.  This  artery 
runs  upward  behind  the  anterior  wall  of  the  abdomen,  and 
unites  by  anastomosis  with  the  lower  extremity  of  the  internal 
mammary  artery.  On  leaving  the  pelvis  the  external  iliac 
takes  the  name  of  \hzfemoral  artery,  gives  off  large  branches 
to  the  muscles  of  the  thigh,  and  on  reaching  the  lower  third 
of  this  region,  becomes  the  popliteal  artery,  or  artery  of  the 
ham.  This  last  gives  off  the  anterior  tibial,  and  then  divides 
into  the  posterior  tibial  and  the  peroneal  artery.  The  anterior 
tibial  at  the  point  of  the  articulation  of  the  foot  with  the  leg 
takes  the  name  of  dorsal  artery  of  the  foot,  and  ramifies  over 
the  upper  surface  of  the  foot;  while  the  peroneal  and  posterior 
tibial,  after  having,  like  the  anterior  tibial,  distributed  branches 
to  the  leg,  terminate  in  the  plantar,  region,  or  sole  of  the  foot 

Veins. — The  veins  carry  the  blood  from  the  extremities  to 
the  heart.  They  are  divided  like  the  arteries  into  two  classes, 
according  as,  filled  with  red  blood,  they  run  from  the  capil- 
laries of  the  lungs  to  the  trunks  of  the  pulmonary  veins — 
which  is  the  lesser  circulation;  or  as  they  carry  the  black 
blood  to  the  venae  cavae — which  is  the  general  circulation. 
The  veins  of  the  liver  and  their  principal  trunk,  the  portal 
vein,  have  sometimes  been  considered  as  also  a  separate 
system;  and  this  distinction  has  also  been  extended  to  those 
of  the  kidneys  and  other  organs. 

The  walls  of  the  veins  are  much  thinner  than  those  of  the 
arteries,  and  are  formed  of  four  tunics,  of  which  the  fourth 
or  internal  one  is  like  that  of  the  arteries;  the  others  are 
formed  of  elastic  or  cellular  fibres,  longitudinal  in  the  third, 
circular  in  the  second,  in  such  a  manner  as  to  present  the 


PRINCIPAL   VEINS.  IOQ 

greatest  resistance.  The  third  and  fourth  coats  form  folds, 
which  when  extended  partially  close  the  vessel.  These  valves 
are  disposed  in  such  a  manner  as  that  when  the  blood  moves 
toward  the  heart  it  presses  them  close  to  the  walls  of  the  veins, 
and  they  are  no  obstacle  to  its  course;  while,  if  it  moves  in  the 
contrary  direction,  they  close  and  prevent  its  return  toward 
the  extremities.  The  veins  are  disposed  in  two  planes. 
Some  are  deeply  placed,  and  accompany  the  arteries,  of  which 
they  are  called  the  companions  (vena  comites  arteriaruni)\ 
others  are  superficial,  and  creep  along  under  the  skin  without 
any  coincidence  with  the  direction  of  the  arterial  vessels. 
Springing  from  the  capillaries,  by  means  of  which  they  com- 
municate with  the  arteries,  the  venous  radicles  unite  more 
rapidly  than  those  of  the  arteries  into  considerable  branches, 
superior  in  numbers  and  total  capacity  to  the  arterial  trunks. 
Many  of  the  arteries,  in  fact,  are  accompanied  by  two  veins 
as  satellites,  of  at  least  equal  calibre;  and  the  superficial  veins 
show  still  greater  disproportion.  In  the  interior  of  the 
cranium  the  veins  are  transformed  into  sinuses  or  canals 
formed  by  the  dura  mater,  which  receive  the  venous  branches 
of  the  brain.  The  veins  are  enveloped  in  their  course  by 
numerous  lymphatic  vessels. 

Principal  veins. — The  superior  and  inferior  vena  cava  are 
to  the  venous  system  what  the  aorta  is  to  the  arterial  system. 

The  superior  vena  cava  receives  the  blood  from  the  head, 
neck,  the  upper  extremities,  and  the  walls  of  the  chest;  it 
opens  into  the  right  auricle  of  the  heart.  It  is  formed  by  the 
two  brachio-cephalic  trunks  and  the  azygos  vein.  Each  of 
these  brachio-cephalic  venous  trunks  unites,  like  the  arterial 
trunks  of  the  same  name,  all  the  principal  veins  of  the  head 
and  the  arms,  which  are  the  two  jugulars,  internal  and  ex- 
ternal, and  the  subclavian. 

The  internal  jugular  corresponds  to  the  carotid  artery;  it 
receives  the  blood  from  the  sinuses  of  the  dura  mater,  from 
the  veins  of  the  head,  of  the  neck,  and  part  of  the  shoulder. 
The  external  jugular  carries  the  blood  from  a  part  of  the 
superficial  veins  of  the  head  to  the  subclavian  vein. 

The  subclavian  vein  corresponds  to  the  artery  of  the  same 
name,  and  receives  the  companion  veins,  and  veins  corre- 


IIO  THE    HUMAN    BODY. 

spending  in  name  to  the  arteries  of  the  upper  limb;  it  is  also 
the  common  trunk  of  the  superficial  veins  of  the  hand,  fore- 
arm, and  arm,  the  principal  of  which  are  the  cephalic  and 
basilic.  This  last  vein  crosses  the  radial  artery  in  the  bend 
of  the  elbow,  and  is  separated  from  it  by  a  tendinous  expan- 
sion of  the  biceps  muscle.  The  cephalic  and  basilic  veins  are 
those  most  commonly  opened  in  blood-letting;  this  operation 
is  rendered  delicate  by  the  situation  of  the  basilic,  which  ex- 
poses the  artery  to  the  danger  of  being  wounded. 

The  azygos  vein  (azygos,  without  a  fellow)  forms  the  com- 
munication between  the  superior  and  inferior  vena  cava.  It 
rises  vertically  in  the  posterior  mediastinum  and  to  the 
right  of  the  spine,  and  about  the  level  of  the  seventh  rib  it 
receives  the  lesser  vena  azygos,  which  comes  from  the  abdomen. 

The  inferior  vena  cava  opens  into  the  right  auricle  under 
the  superior  vena  cava.  It  is  the  common  trunk  of  all  the 
veins  coming  from  the  parts  below  the  diaphragm,  and  is 
formed  by  the  union  of  the  two  iliac  trunks,  companions  of 
the  iliac  arteries;  it  runs  up  vertically  to  the  right  of  the 
spine  as  companion  vein  to  the  aorta,  and  receives  the  veins 
of  the  abdomen.  Its  primitive  branches,  the  iliac  trunks,  are 
formed  by  the  union  of  the  veins  of  the  pelvic  cavity  and  of 
the  lower  extremities,  companions  of  the  arteries  of  the  same 
name.  Among  the  superficial  series  of  veins,  which  are  also 
tributaries  to  the  main  iliacs,  are  the  external  and  internal 
saphenons  veins,  which  run  from  the  foot  to  the  top  of  the 
thigh.  These  two  veins  are  plainly  visible  on  the  front  of 
the  ankle  and  on  the  calf. 

Portal  system. — An  arrangement  of  veins  peculiar  to  the 
abdomen,  and  especially  to  the  liver,  is  designated  by  this 
term.  The  portal  vein  is  formed  by  the  union  of  the  veins 
of  the  mesentery,  spleen,  stomach,  and  intestine;  it  trans- 
mits the  blood  from  these  organs  to  the  liver,  from  whence 
it  is  poured  into  the  inferior  vena  cava. 

Lymphatic  vessels  and  ganglia. — This  is  the  name  given 
to  a  special  circulatory  apparatus  composed  of  very  delicate 
vessels  with  transparent  walls  and  Q{ ganglia  or  glands,  which 
appear  to  be  formed  by  these  vessels,  some  of  which  ter- 
minate in  and  others  spring  from  them. 


MECHANISM    OF    THE    CIRCULATION.  Ill 

The  lymphatic  vessels  have  a  very  irregular  ^course,  and 
exhibit  numerous  swellings  which  are  owing  to  valves.  They 
exist  in  every  part  of  the  body,  and  transport  the  chyle  and  the 
lymph,  drawn  by  their  microscopical  roots  from  the  surface  of 
the  mucous  membrame  of  the  intestines,  or  from  the  tissues 
of  the  organs.  They  accompany  the  blood-vessels  in  their 
course,  especially  the  veins,  and  they  are  also  found  in  great 
numbers  at  the  surface  of  the  body  in  regions  abounding  in 
subcutaneous  veins,  as  in  the  limbs,  face,  and  neck.  They 
are  very  numerous  in  the  mesentery  and  around  the  intes- 
tines; they  unite  in  two  principal  trunks  or  reservoirs,  one 
of  which  is  the  thoracic  duct,  which  rises  through  the  chest  at 
the  left  of  the  spine,  and  opens  into  the  left  subclavian  vein, 
the  other  is  called  the  great  right  lymphatic  vessel  (ductus 
lymphaticus  dexter),  which  runs  parallel  with  the  first,  and 
opens  into  the  right  subclavian  vein. 

Mechanism  of  the  circulation. — Galen  was  the  first  to  dis- 
cover that  the  arteries  contained  blood  and  that  they  com- 
municated with  the  veins,  but  he  went  no  farther  than  this. 
In  1553  Michael  Servetus,  guessing,  so  to  speak,  the  pheno- 
mena of  the  pulmonary  circulation,  indicated  very  exactly 
the  course  of  the  blood  and  its  elaboration  in  the  lungs  by 
contact  with  the  air.  But  the  doctrine  of  Servetus  rested 
neither  upon  proof  nor  experiment,  it  resulted  from  a  sort  of 
intuitive  perception  of  the  facts,  and  he  was  not  aware  either 
of  the  impulsive  force  of  the  heart  or  the  action  of  its  valves. 

Other  physiologists,  like  Servetus,  had  glimpses  of  the 
truth  and  added  new  discoveries  to  his ;  in  fact,  most  of  the 
phenomena  of  the  circulation  had  been  suspected  or  indi- 
cated at  the  commencement  of  the  seventeenth  century,  but 
all  the  knowledge  on  the  subject  was  but  a  chaos  of  facts 
and  reasonings  without  unity,  and  often  contradictory.  It 
required  the  genius  of  Harvey  to  extract  from  this  chaos  a 
simple  and  irrefutably  demonstrated  system. 

Movements  and  sounds  of  the  heart. — The  heart,  the  prin- 
cipal agent  of  the  circulation's  the  source  of  movements  which 
are  not  under  the  control  of  the  will,  but  which  are  constantly 
influenced  by  moral  impressions  and  by  sensations.  These 
movements  consist  in  the  alternate  contraction  and  relaxa- 


112  THE    HUMAN    BODY. 

tion  of  the  walls  of  the  heart,  that  is  in  the  opening  and 
shutting  of  its  cavities.  The  ventricles  contract  simultane- 
ously, then  to  this  contraction  succeeds  a  period  of  relaxa- 
tion, during  which  the  auricles  in  their  turn  contract,  to  relax 
during  a  new  contraction  of  the  ventricles.  The  dilating 
movement  is  called  the  diastole,  and  the  contracting  the 
systole.  During  the  diastole  the  blood  flows  into  the  cavities 
of  the  heart,  to  be  expelled  by  the  systole;  the  contraction 
cf  the  auricles  forces  it  into  the  ventricles,  that  of  the 
ventricles  throws  it  into  the  aorta  and  the  pulmonary  artery. 

The  contraction  of  the  ventricles  modifies  the  form  of  the 
heart.  Its  transverse  circumference  is  ellipsoid  during  the 
diastole,  and  becomes  circular  during  the  systole;  the 
antero-posterior  diameter  being  thus  greater,  the  point  of 
the  heart  strikes  the  anterior  wall  of  the  chest,  and  if  the  ear 
be  applied  to  this  point,  a  dull  sound  will  be  heard  at  the 
moment  of  the  shock,  and  about  half  a  second  after,  a  clearer 
sound  is  heard,  coincident  with  the  relaxation  or  the  diastole 
of  the  ventricles.  The  mechanism  of  these  sounds  has  been 
variously  explained;  they  seem  to  be  owing,  the  first  to  the 
sudden  closing  of  the  tricuspid  and  mitral  valves  at  the 
moment  when  the  ventricular  systole  throws  the  blood  into 
the  aorta  and  pulmonary  artery;  the  second  to  the  closing 
of  the  sigmoid  valves  during  the  ventricular  diastole,  under 
the  influence  of  the  elasticity  of  the  arteries,  which  tends  to 
cause  a  reflux  of  the  column  of  blood. 

The  alternation  of  the  systole  and  diastole  constitute  the 
rhythm  and  regularly  marked  beating  of  the  heart  which 
makes  itself  heard  and  felt  through  the  walls  of  the  chest. 
We  will  follow  these  movements  in  their  evolution  and  the 
blood  in  its  course. 

Arterial  circulation. — The  left  ventricle,  in  contracting, 
pushes  the  red  blood  which  it  contains  in  the  direction  of 
the  auriculo-ventricular  orifice  and  toward  the  orifice  of  the 
aorta, — but  the  mitral  valve  is  so  placed  that  it  closes  under 
the  impulse  of  the  moving  blood,  which  is  thus  forced  into 
the  aorta  and  from  thence  into  all  the  arteries,  in  which  its 
motion  is  caused  by  the  triple  action  of  ventricular  contrac- 
tion, and  of  the  elasticity  and  contractility  of  the  arterial 


ARTERIAL    CIRCULATION.  1 13 

walls.  In  vessels  of  a  certain  calibre  this  movement  is  jerk- 
ing and  rhythmical,  precisely  like  that  of  the  heart,  and  if  we 
place  the  finger  on  the  course  of  an  artery  we  feel  the  shock 
of  the  blood,  or  the  pulse.  The  pulse  and  the  beating  of 
the  heart  are  synchronous,  that  is,  they  take  place  simultane- 
ously, or  rather  with  an  interval  so  short  as  to  be  impercep- 
tible. But  in  proportion  as  the  blood  advances  through  the 
arterial  ramifications,  the  numerous  changes  of  direction  which 
it  undergoes  and  the  friction  between  it  and  the  walls  of  the 
vessels  diminish  the  force  of  its  impulsion;  and  at  last,  on 
reaching  the  capillary  vessels  it  flows  continuously  and  with- 
out shock. 

In  examining,  under  a  microscope,  a  vascular  membrane 
belonging  to  a  living  animal,  the  circulation  of  the  blood 
through  the  capillaries  is  plainly  visible.  The  largest  of 
these  canals  allow  the  column  of  blood  to  pass  rapidly,  in 
the  smallest  ones  its  course  is  slow  and  the  blood-globules 
can  only  pass  one  by  one;  they  float  in  a  transparent  fluid, 
and  sometimes  a  globule  becomes  entangled  obliquely  across 
the  calibre  of  the  vessel  and  stops  until  another  comes  to 
push  it  forward.  Malpighi  was  the  first  to  verify  in  this 
manner  the  accuracy  of  Harvey's  theory,  forty  years  after  it 
had  been  propounded  by  the  illustrious  English  physiologist. 

The  different  causes,  therefore,  which  accelerate  or  retard 
the  contractions  of  the  heart,  influence  the  motion  of  the 
blood  in  the  arteries;  and  farther,  the  contractility  of  these 
vessels  may  be  influenced  by  local  causes,  and  the  movement 
of  the  blood  is  modified  so  as  to  be  either  retarded  or 
quickened,  as  they  are  contracted  or  relaxed.  In  the  first 
case  the  afflux  of  blood  is  not  sufficient  to  excite  the  organs, 
which  become  sluggish  and  partially  paralyzed;  in  the  second 
it  is  so  great  as  to  cause  an  abnormal  activity  of  the  function. 
And  lastly,  we  all  know  that  the  repose  or  action  of  the 
muscles  has  the  effect  of  retarding  or  accelerating  the  circula- 
tion, general  or  local,  which,  in  the  course  of  time,  results  in 
the  diminution  or  increase  of  the  muscular  strength. 

It  is  in  the  capillaries,  in  fact,  that  arterial  blood  yields  to 
the  tissues  the  elements  of  which  it  is  composed,  and  which 
it  delivers  to  them  for  assimilation,  in  order  to  receive  in 

3 


114  THE    HUMAN    BODY. 

exchange  the  disassimilated  particles  which  are  to  be  rejected 
from  the  system  or  submitted  to  a  fresh  elaboration.  A 
living  and  nourishing  fluid,  it  carries  to  the  organs  life,  heat, 
and  the  elements  of  nutrition. 

Venous  circulation. — After  passing  through  the  capillary 
vessels,  the  blood  passes  into  the  venous  radicles.  At  its 
entrance  into  the  aorta  and  during  its  course  through  the 
arterial  system,  it  was  of  a  brilliant  red  colour,  now  it  has 
become  dark;  the  arterial  or  red  blood  is  changed  to 
venous  or  black  blood;  deprived  of  the  greater  portion  of 
its  constituent  elements  it  returns  to  their  source  for  a  fresh 
supply. 

The  blood  moves  in  the  veins  from  the  impulsion  received 
originally  from  the  heart;  this  force  is  designated  by  the  term 
vis  a  tergo,  because  it  is  exerted  behind  the  fluid  column. 
The  elasticity  of  the  veins,  and  their  contractility  also,  con- 
tributes to  urge  the  blood  along  in  its  return  towards  the 
heart,  but  it  is  the  valves  which  most  effectually  second  the 
cardiac  impulse  by  opposing  the  reflux  of  the  blood  toward 
the  arteries.  If  a  moderately  tight  ligature  be  placed  around 
the  arm,  the  veins  begin  to  swell  because  of  the  afflux  of 
blood,  which  can  neither  go  on  toward  the  heart  because  of 
the  ligature,  nor  return  toward  the  arteries  because  of  the 
valves  which  oppose  it  in  that  direction.  If  the  finger  be  now 
passed  lightly  over  the  course  of  a  vein  in  a  direction  op- 
posed to  the  circulation,  the  little  nodules  which  mark  the 
projections  caused  by  the  distended  valves  are  easily  dis- 
tinguished. Thanks  to  the  play  of  these  valves,  any  pressure 
upon  the  veins,  from  muscular  contraction,  or  whatever 
cause,  can  only  carry  the  blood  toward  the  heart,  while  with- 
out them  it  would  be  impelled  indiscriminately  one  way  or 
the  other.  Therefore  the  valves  are  more  numerous  in  the 
veins  which  are  connected  with  the  muscles;  in  the  deep 
veins  of  the  limbs,  for  example,  than  in  those  which  creep 
along  under  the  skin. 

Gravitation  affects  the  movement  of  the  venous  blood, 
which  is  much  less  rapid  than  that  of  arterial  blood.  When 
the  hands  hang  down  for  a  long  time  as  in  walking,  they 
swell  so  much  that  the  flexion  of  the  fingers  is  difficult,  and 


VENOUS    AND    PULMONARY    CIRCULATION.  115 

it  is  the  same  with  the  feet  and  legs  after  long-continued 
standing,  and  varicose  veins  appear  on  the  limbs  of  persons 
whose  profession  obliges  them  to  remain  on  their  feet. 

In  following  the  course  of  the  blood  on  its  return  to  the 
heart,  we  mid  a  venous  system  belonging  to  the  liver  and 
intestines;  the  portal  system — to  which  reference  has  already 
been  made — which  carries  the  venous  blood  from  the  diges- 
tive canal  and  from  the  spleen  to  the  liver.  This  system  is 
remarkable  from  the  fact  that  it  is  ramified  at  both  ex- 
tremities; at  the  intestinal  extremity  the  radicles  or  roots, 
and  at  the  hepatic  the  branches,  are  found.  From  this  it  has 
been  inferred  that  the  bile  is  secreted  from  the  blood  of  the 
portal  vein  and  not  from  the  blood  of  the  hepatic  artery;  but 
this  question  still  remains  unsettled. 

The  inferior  vena  cava,  after  receiving  the  blood  from  the 
lower  regions  of  the  body,  turns  toward  the  heart  like  the 
superior  vena  cava,  but  before  reaching  it,  the  blood  receives 
by  the  subclavian  veins  the  lymph  and  chyle  which  have 
been  brought  to  it  by  the  two  grand  trunks  of  the  lymphatic 
system;  the  elements  of  nutrition  drawn  from  the  intestine 
come  to  replace  those  which  have  just  been  given  up  for 
assimilation.  Thus  partially  reconstituted,  the  blood  pours 
back  through  the  venae  cavae  into  the  right  auricle  of  the 
heart,  and  the  auricle  by  contracting  throws  it  into  the  right 
ventricle. 

At  last  the  blood  has  returned  to  the  heart,  and  although 
it  is  enriched  by  the  assimilable  products  of  digestion,  it  is 
still  incomplete,  and  must  be  transformed  in  order  to  become 
perfect  arterial  blood,  while  at  the  same  time  the  combustion 
of  a  portion  of  its  principles  will  produce  the  heat  which  is 
soon  to  be  distributed  to  the  organism.  It  is  in  the  lungs 
that  this  elaboration  of  the  blood  is  to  take  place — hematosis 
or  sanguification. 

Pulmonary  circulation. — The  right  ventricle  contracts,  and 
the  flood  of  venous  blood  closes  the  tricuspid  valve,  and 
passes  into  the  pulmonary  artery.  This  artery  and  all  its 
ramifications  contain  black  or  venous  blood,  while  the  pul- 
monary veins,  as  we  shall  soon  see,  convey  red  or  arterial 
blood ;  it  is  therefore  to  their  direction,  from  the  heart  to  the 


THE    HUMAN    BODY. 


lungs,  or  from  the  lungs  to  the  heart,  that  the  vessels  of  the 
pulmonary  circulation  owe  their  names.  The  pulmonary 
artery,  like  the  aorta,  is  provided  at  its  orifice  with  three 
valves,  called  sigmoid  or  semi-lunar  valves.  From  the  right 
ventricle  to  the  ramifications  of  the  pulmonary  artery  the 
blood  has  but  a  short  distance  to  pass,  and  it  meets  with  no 
resistance  at  all  comparable  to  that  encountered  in  the  sys- 
temic arterial  circulation.  The  walls  of 
the  right  ventricle  therefore  are  much 
thinner  than  those  of  the  left,  and  con- 
sequently have  less  power.  In  the  ca- 
pillaries of  the  lungs  the  motion  of  the 
blood  varies  in  quickness  according  as 
the  respiration  is  easy,  or  retarded  by 
any  obstacle,  or  by  the  presence  of  air 
unfit  for  the  performance  of  the  respi- 
ratory functions.  The  capillaries  are 
distributed  through  the  substance  of  the 
lungs  in  such  a  manner  that  they  cor- 
respond to  the  pulmonary  cells.  (See 
Respiration,  p.  92.)  It  is  in  these  ulti- 
mate divisions  of  the  lungs  that  the  oxy- 
gen of  the  air  combines  with  the  venous 
blood  charged  with  carbonic  acid,  and 
transforms  it  into  arterial  blood.  The 
reddish-brown  globules  of  the  venous 
_____  o____^  _._  blood  take  a  vermilion  colour  from 
gram  of  the  course  'of  the  COntact  with  the  oxygen,  and  charged 

blood  in  the  circulation.  .  .  1111  • 

with  oxygen,  the  blood  penetrates  into 

,  ,'.    ,  r       -\ 

the  radicles  of  the  pulmonary  veins, 
obeying  the  original  impulse,  the  vis  a 
tergo,  as  in  the  general  venous  system, 
but  with  greater  quickness.  It  is  now  carried  back  to  the 
left  auricle,  which  immediately  transmits  it  to  the  ventricle, 
where  its  circular  course  ends,  only  to  commence  again 
immediately.  The  circulation  may  be  divided  into  two 
simultaneous  periods,  or,  as  has  been  already  stated,  the  ima- 
ginary circle  through  which  the  blood  passes  is  composed  of 
two  unequal  segments  described  by  the  fluid  column.  The 


Fig.  28.  —  Imaginary  dia- 
gram of  the  course  of  th 
ilood  in  the  circulation. 

A.    Course  of  the   venous 
•  of 


arterial 


ACCELERATION  AND  RETARDATION  OF  PULSE.    II J 

upper  segment  indicates  the  pulmonary  or  lesser  circulation, 
the  lower  the  general  or  systemic  circulation. 

Influences  which  retard  or  accelerate  the  beating  of  the  heart. 
— In  an  adult  in  a  normal  condition,  the  heart  beats  about 
sixty  times  a  minute,  and  the  pulse  consequently  indicates 
the  same  number  of  pulsations,  but  diverse  causes  may 
augment  or  diminish  the  frequency  of  these  movements. 
They  become  more  frequent  during  digestion,  and  under  the 
influence  of  alcohol,  coffee,  or  other  excitants;  abstinence, 
on  the  contrary,  retards  them.  Intellectual  labour  also  accel- 
erates the  action  of  the  heart,  but  the  heart  is  calmer  during 
sleep,  and  shares  in  a  measure  the  repose  of  the  other  organs. 
An  unlocked  for  sight,  a  word  striking  the  ear,  or  a  thought 
crossing  the  mind,  will  cause  strong  and  rapid  pulsations. 
Eristratus  discovered  the  cause  of  the  malady  which  threat- 
ened the  life  of  Antiochus,  by  placing  his  hand  on  the  heart 
of  the  young  prince  at  the  moment  that  Stratonicea  appeared 
before  him.  The  pulse  is  accelerated  also  by  muscular 
exercise,  and  by  violent  efforts.  But  in  this  case  the  cause 
is  complex,  for  the  respiration  is  also  more  frequent,  and  this 
function  is  one  of  those  which  have  most  influence  on  the 
circulation.  In  ordinary  breathing,  each  inspiration  gives 
more  force  to  the  blood  in  the  arteries,  and  if  the  respiration 
becomes  more  hurried  it  is  recognizable  in  the  pulse.  If,  on 
the  contrary,  respiration  is  suspended  or  imperfect,  the  circu- 
lation is  retarded,  and  the  pulse  beats  with  less  force;  in  a 
word,  in  most  physiological  conditions  there  is  a  constant 
relation  between  the  respiratory  movements  and  the  beating 
of  the  heart.  The  alternate  expansion  and  contraction  of 
the  walls  of  the  chest  are  therefore  one  of  the  principal 
causes  which  affect  the  circulation,  by  facilitating  the  afflux 
of  blood  to  the  thoracic  cavity  and  insuring  its  expulsion 
from  it. 

The  pressure  of  the  atmosphere  also  influences  the  beating 
of  the  heart,  but  only  under  certain  conditions.  It  is  not  un- 
common to  find  in  the  high  valleys  among  the  Alps  men  whose 
pulse  beats  between  fifty  and  sixty  times  a  minute — this  infre- 
quency  is  perhaps  more  common  among  mountaineers  who 
live  at  an  altitude  of  3280  feet  or  more,  than  in  less  elevated 


Il8  THE    HUMAN    BODY. 

countries.  We  may  consider  therefore  that  the  altitude  has 
no  influence  upon  persons  who  have  long  lived  at  a  given 
level.  But  if  we  rise  rapidly  to  a  great  height,  the  pulse 
quickens  very  sensibly.  Aerostatic  ascensions  and  mountain 
journeys  furnish  the  proof  of  this.  It  is  not  to  locomotion 
or  to  muscular  effort  that  this  quickening  of  the  pulse  can 
be  attributed  in  the  aeronaut  or  the  traveller  on  horseback, 
but  it  is  chiefly  due  to  the  greater  frequency  of  respiration  in 
an  atmosphere  of  lesser  density.  The  diminution  of  the 
pressure  of  the  atmosphere  conduces  also  to  the  same  effect 
by  relaxing  the  vessels;  but  the  fall  in  temperature  in  pro- 
portion to  the  rise  in  elevation  seems  to  neutralize  this  last 
effect  by  the  contraction  of  the  tissues  which  it  induces.  (See 
Respiration,  p.  99.) 

The  establishment  of  the  fact,  that  an  increase  in  the 
pressure  of  the  atmosphere  diminishes  the  frequency  of  the 
pulse  is  due  to  the  observations  of  Pravaz  and  Tabarie.  Both 
these  authors  state  that  the  pulse  falls  to  fifty  and  even  to 
forty-five  pulsations  per  minute  when  the  subjects  are  placed 
in  an  apparatus  for  compressing  air,  and  the  pressure  is 
increased  to  that  of  two  atmospheres  and  over.  Results 
entirely  contrary  were  observed  by  M.  Francois  in  the  tubes 
containing  compressed  air  which  he  used  in  building  the 
bridge  at  Kehl  in  1860.  This  physician  observed  that  the 
pulse  invariably  quickened  in  the  labourers  employed  upon 
this  work  under  a  pressure  of  about  two  atmospheres. 
Other  observations  by  M.  Hermel  establish  the  fact  that  the 
pulse  is  sometimes  retarded,  and  sometimes  quickened  in 
compressed  air  to  one  hundred  and  fifty  in  a  minute.  The 
phenomena  observed  in  men  who  work  in  compressed  air 
seem  to  be  due  to  complex  causes,  among  which  we  must 
note  the  vitiation  of  the  air  from  deficient  renewal. 

We  shall  not  here  discuss  the  numerous  causes  which  may, 
in  pathological  conditions,  influence  the  circulation. 


CHAPTER  X. 


Nervous  system.  —  Cerebro-spinal  nervous  centre.  —  Cerebrum.  —  Cere- 
bellum.— Isthmus  of  the  encephalon. — Medulla  oblongata. — Spinal  cord. 
— Membranes;  dura  mater,  arachnoid,  pia  mater. — Nerves;  cranial 
nerves,  spinal  nerves,  great  sympathetic. — Functions  of  the  nervous 
system;  functions  of  the  spinal  nerves  of  motion  and  of  sensation;  func- 
tion of  the  cranial  nerves;  functions  of  the  spinal  marrow. — functions 
of  the  encephalon ;  medulla  oblongata,  pons  Varolii,  peduncles  of  the 
cerebrum  and  cerebellum,  corpora  quadrigemina,  pineal  gland,  optic 
thalami,  cerebrum  and  cerebellum. — Functions  of  the  great  sympathetic. 
• — Reflex  pouter.  — Nerve  force.  — Memory. 


/    The  nervoiis  system  comprises  the  cerebrum  and  cerebellum, 
(  the  spinal  cord,  and  the  nerves.     It  is  divided  into  two  por- 
tions, the  one  central,  and  the  other  external  or  peripheric. 
The  first  has  received  the  name  of  the  cerebro-spinal  nervous 
centre,  because  it  is  constituted  by  the  organs  which  form  the 

,  encephalon  and  by  the  spinal  cord.  The  second  is  the  whole 
of  the  nerves  proper.  Starting  from  the  nervous  centre,  of 
which  they  are  the  expansion,  they  are  distributed  to  the 
whole  body.  They  transmit  motive  or  functional  impulses 
from  the  nervous  centre  to  every  part  of  the  organism;  and 
the  impressions  of  sensibility  from  the  periphery,  that  is  to 
say  from  the  different  points  of  the  body  to  the  nervous 
centre. 

The  cerebro-spinal  nervous  centre  appears  in  the  form  of  a 
soft  pulpy  symmetrical  trunk.  Its  upper  portion  is  an  oval 
enlargement  contained  within  the  cranium,  and  is  called 
ths  encephalon  or  brain.  The  lower  portion  is  elongated 
on  leaving  the  cranium  in  the  form  of  a  spindle — it  is  the 
spinal  marrow,  and  is  contained  in  the  vertebral  canal. 
Brain. — This  is  the  term  commonly  applied  to  all  the 


120 


THE    HUMAN    BODY. 


Fig.  29.— Cerebro-spinal  nervous 
centre. 


parts  of  the  encephalon,  which  are 
the  brain  proper,  or  cerebrum;  the 
cerebellum,  or  little  brain;  the  isth- 
A  mus  of  the  encephalon,  or  the  at- 
tachment which  joins  the  differ- 
ent parts  together;  and  the  bulb 
of  the  spinal  cord,  or  medulla  ob- 
longata. 

The  brain  occupies  nearly  all 
the  cavity  of  the  cranium,  which 
fits  it  like  a  mould.  ( It  is  oval  in 
form,  flattened  on  its  inferior  sur- 
face, which  rests  on  the  base  or 
floor  of  the  skull;  its  anterior  or 
frontal  extremity  is  smaller  than 
the  posteriory  Its  greatest  trans- 
verse diameter  is  the  space  be- 
tween the  temporal  fossae.  It  is 
divided  in  the  median  line  by  the 
great  fissure  running  from  behind 
forward  vertically  through  part  of 
its  depth  into  two  portions,  called 
the  hemispheres  of  the  brain.  This 
j  division  is  complete  in  front,  at 
/  the  back  and  on  the  top,  but  the 
/  two  parts  are  united  at  the  middle 
and  lower  third  by  the  corpus  cal- 
losum,  the  peduncles,  and  some 
other  parts  situated  in  the  middle 
line. 

A  lateral  fissure,  called  the  fis- 


A.  Cerebrum-— or  brain  proper. 

B.  Cerebellum — lesser  brain. 

C.  Pons  l-'arolii. 

D,  D.  Spinal  marrow,  shoiving  the  origin 

of  the  spinal  nerves. 

E,  E.  Spinous  processes  of  the  vertebra. 

F.  Seventh  cervical  vertebra. 

G.  Twelfth  dorsal  vertebra. 
H.  Fifth  lumbar  vertebra. 

I.  Sacrum. 


Fig.  30. — Nervous  System. 


THE    BRAIN.  123 

sure  of  Sylvius,  divides  each  hemisphere  obliquely  into  two 
lobes,  the  anterior  and  posterior. 

The  surface  of  the  hemispheres  is  broken  with  deep  irregular 
suld  or  furrows,  which  define  the  oblong  rounded  winding 
ridges,  themselves  subdivided  by  secondary  furrows,  and 
called,  from  their  analogy  to  the  windings  of  the  smaller 


Fig.  31. — Upper  surface  of  the  brain. 
A,  A.  Great  fissure.  B,  B.  Cerebral  hemispheres. 

intestine,  the  convolutions  of  the  brain.  Some  of  these  are 
always  present,  and  appear  symmetrically  in  both  hemi- 
spheres; others  are  variable,  not  found  on  both  sides,  differing 
in  length,  breadth,  and  in  projection.  These  convolutions 
cover  the  external,  superior,  and  inferior  surfaces  of  both 
hemispheres,  and  are  continued  also  on  their  internal  surface 
the  whole  length  of  the  great  fissure,  and  of  the  fissure  of 
Sylvius. 


124 


THE    HUMAN -BODY. 


•  The  lower  surface  or  base  of  the  brain  presents  an  ex- 
tremely complicated  relief.  In  front,  and  on  the  sides,  there 
are  numerdus  convolutions.  Towards  the  centre  we  find. 


Fig.  32. — Lower  surface  of  the  brain. 


A.  Anterior  lobe. 

A'.  Fissure  of  Sylvius. 
A".  Middle  lobe. 
A'".  Posterior  lobe. 

C.  Cerebellum,  or  little  brain. 
M<7.  Medulla  oblongata. 
PV.  Pans  Varolii. 
T/.  The  pitrdtary  body. 
i-i.  First  pair,  or  olfactory  nerves. 
2-2.  Second  pair,  or  optic  nerves. 
3-3.  Third  pair,    or  common    motor 

nerves  of  the  eye. 
4-4.  Fourth  pair,  or  pathetic  nerves. 


5-5.  Fifth  pair,  or  trigeminal. 

6-6.  Sixth  pair,  or  abducent  nerves  of  the 

eye. 
7-7.  Seventh  pair —a,  Facial  nerve. 

b,  A  uditory  net  ve. 

8-8.  Righth   pair- — a.,.  Glosso-pharyngcal 
nerve. 

b,  Pneumo-gastric 

nerve.   • 

c,  Spinal-accessory 

nerve. 
9-9.  Ninth  pair,  or  hypoglossal  nerves. 


among  other  important  details,  the  olfactory  nerves  on  each 
side  of  the  great  fissure ;  the  chiasma,  or  crossing  of  the  optic 
nerves;  $h& pituitary  body;  the  tuber  cinereum,  or  ash-coloured 
body;  the  corpora  mammillaria,  or  mammillar  bodies;  and  the 


STRUCTURE    OF    THE    BRAIN.  125 

peduncles  of  the  brain,  which  are,  as  it  were,  the  roots  of  that 
organ  uniting  it  to  the  .other  parts  of  the  encephalon;  the 
pons  Varolii,  or  annular  protuberance;  the  medulla  oblongata; 
and  the  origins  of  the  cranial  nerves. 

The  brain,  as  well  as  all  the  divisions  of  the  cerebro- 
spinal  nervous  centre,  is  composed  of  two  distinct  sub- 
stances :  the  gray  or  cortical  substance,  the  first  on  account  of 
its  colour,  and  the  second  because  it  is  on  the  surface  of  the 
brain,  like  a  bark  (cortex);  and  the  white  substance,  which  is 
everywhere  completely  surrounded  by  the  gray. 

The  gray  substance  is  pulpy  and  less  consistent  than  the 
white.  It  is  disposed  around  the  principal  organs  of  the  ence- 
phalon in  a  superficial  layer,  and  enters  into  their  substance 
in  masses  varying  in  form  and  volume.  The  white  substance 
is  filamentous  in  texture,  and  exhibits,  according  to  the  region, 
bundles,  cords,  or  layers,  composed  of  slender  fibres,  which 
are  alike  in  the  nervous  centres  and  in  all  the  nerves  of  the 
body.  The  white  greatly  exceeds  the  gray  substance  in  total 
amount. 

On  laying  open  the  brain  we  find  it  is  composed  of  a 
central  nucleus — or  knot — unique  and  symmetrical,  a  sort  of 
terminal  enlargement  of  the  nervous  axis,  and  of  two  hemi- 
spheres united  by  this  central  portion,  of  which  they  are,  as 
it  were,  a  sort  of  double  expansion.  This  central  nucleus 
comprises  parts  very  complicated  in  their  structure  and  in 
their  relative  positions.  The  principal  ones  are  the  thalamus 
opticus'Qi  optic  bed,  the  corpora  striata  or  striated  bodies,  and 
the  corpus  callosum  or  hard  body.  All  these  subdivisions  of 
the  cerebral  centre  are  united  to  each  other,  to  the  peduncles, 
and  to  the  hemispheres.  Thus  the  corpus  callosum,  which 
serves  as  an  envelope  of  the  cerebral  centre,  receives  fibres 
from  the  peduncles  and  from  the  optic  bed,  prolongs  its 
edges  into  the  substance  of  the  hemispheres,  between  which 
it  is,  as  already  stated,  the  principal  means  of  union. 

In  the  substance  of  the  cerebral  centre  there  are  three 
cavities,  called  the  ventricles  of  the  brain;  two  are  lateral, 
and  the  third  or  middle  is  placed  on  the  median  line;  they 
communicate  with  each  other,  and  are  bathed  with  a  serous 
fluid  analogous  to  that  which  lubricates  the  spinal  cord.  On 


126 


THE    HUMAN    BODY. 


the  median  line  and  behind  the  posterior  commissure  of  the 
middle  ventricle  is  a  little  body  nearly  conical,  which  anato- 
mists have  named  the  pineal  gland  or  conarium,  from  its  re- 
semblance to  a  pine-cone. 

A  mass  of  white  substance  forms  the  central  portion  of 


Fig-  33. — Section  of  the  cncephalon  in  the  median  line. 


A.  Plane  of  the  great  fissure. 

B.  Corpus  callosum. 

C.  Optic  bed. 

D.  Pans   Varolii,  wider  which  is  seen 

the  medulla  oblongata. 


E.  Spinal  cord  continued,  from   the  me- 

dulla oblongata. 

F.  Section    of  cerebellum,   showing    tJie 

"tree  of  life" 

G.  Left  hemisphere  of  the  cerebellum. 


both  hemispheres,  and  this  is  covered  over  in  every  part  by 
the  gray  or  cortical  substance. 

The  brain  is  composed  then,  essentially,  of  a  central 
nucleus,  and  two  great  lobes  or  hemispheres.  The  several 
parts  of  this  nucleus  differ  in  their  texture,  in  the  proportion 
of  the  gray  and  white  substances,  and  in  the  disposition  of 
these  two  substances  in  their  tissues;  but  they  all  present 
fibres  which  are  common  to  all,  which  penetrate  and  unite 
them  before  extending  to  the  two  hemispheres. 

The  mass  of  the  entire  encephalon  is  proportionally  greater 


WEIGHT  OF  BRAIN CEREBELLUM.          127 

in  some  species  of  animals,  but  none  approaches  man  in  the 
size  of  the  brain  proper.  If  man  holds  the  first  rank  in 
creation,  he  owes  his  position  to  this  admirable  instrument 
of  the  soul,  to  this  mysterious  medium  between  the  external 
world  and  the  thinking  being. 

The  volume  of  the  brain  is  considerable  from  the  first 
stages  of  existence,  and  larger  in  proportion  in  the  new- 
born infant  than  in  the  adult.  It  is  independent  of  sex 
and  of  the  size  of  individuals.  The  weight  of  the  brain  in 
the  adult  varies,  according  to  Cruveilhier,  from  35  oz.  to 
52  oz. 

The  brain  is  symmetrical,  but  less  constantly  so  than  some 
other  portions  of  the  nervous  centre,  and  there  is  often  a 
notable  disproportion  between  the  two  hemispheres  without 
there  having  been  any  indication  whatever  of  it  during  life. 
This  want  of  symmetry  was  very  marked  in  the  brain  of 
Bichat,  and  this  is  a  striking  proof  that  such  a  conformation 
does  not  necessarily  have  an  unfavourable  influence  on  the 
intellectual  faculties,  as  was  thought  by  this  illustrious 
anatomist. 

The  cerebellum  or  little  brain  lies  in  the  inferior  occipital 
fossae,  that  is  to  say,  in  the  posterior  and  inferior  portion  of 
the  cranium,  and  it  is  covered  by  the  posterior  lobes  of  the 
cerebrum.  It  is  an  ellipsoid  in  form,  flattened  from  the  top 
downward,  with  its  large  extremity  behind,  and  its  greater 
diameter  transverse.  It  is  symmetrical,  and  is  composed 
of  a  middle  lobe  and  two  lateral  lobes  or  hemispheres. 

On  the  upper  surface  of  the  cerebellum  is  a  protuberance, 
extending  from  the  front  backwards ;  it  is  formed  by  the 
middle  lobe,  and  named  from  its  peculiar  appearance  the 
superior  vermiform  process.  The  lateral  lobes  form  an  in- 
clined plane  on  either  side. 

The  lower  surface  fits  into  the  occipital  fossae,  and  forms 
two  rounded  lobes  separated  by  a  furrow,  which  widens  in- 
front  to  receive  the  spinal  bulb.  About  the  middle  of  it  is 
seen  the  inferior  vermiform  process,  the  lower  surface  of  the 
middle  lobe  which  unites  the  two  hemispheres. 

The  whole  surface  of  the  cerebellum  is  furrowed  with 
curved  and  projecting  lines,  which  give  it  a  wrinkled  appear- 


128  THE    HUMAN    BODY. 

ance  (fig.  32,  p.  124).  These  lines  or  folds  are  all  of  about 
the  same  width,  and  are  parallel  through  a  portion  of  their 
course,  and  then  they  form  acute  angles,  and  are  collected 
in  fascicles,  which  point  transversely  downward  or  backward, 
and  divide  the  hemispheres  into  segments,  which  are  divided 
and  subdivided  into  layers. 

The  cerebellum  is  composed,  like  the  cerebrum,  of  white 
and  gray  substance,  with  the  addition  of  a  yellowish  substance 
interposed  in  layers  between  the  two  others.  Each  hemi- 
sphere is  formed  of  a  central  nucleus,  around  which  the  seg- 
ments develop  themselves.  The  layers  of  these  segments 
are  in  juxtaposition  like  the  leaves  of  a  book;  the  white  sub- 
stance is  in  the  centre;  then  comes  a  layer  of  the  yellow 
matter,  and  over  these  the  gray  substance.  If  we  make  a 
vertical  section  of  the  cerebellum,  the  alternating  layers  of 
the  three  substances  of  which  it  is  composed  are  seen  forming 
a  series  of  ramifications  which  spring  from  a  common  trunk : 
this  has  been  named  the  arbor  vita  or  tree  of  life  (fig.  33, 
p.  126).  At  the  nucleus  or  knot,  the  peduncles  of  the  cere- 
bellum terminate ;  they  are  three  in  number  on  either  side, 
and  serve  to  attach  it  to  the  other  parts  of  the  encephalon. 
Near  the  point  where  these  different  parts  unite,  there  is  a 
cavity  which  is  partly  circumscribed  by  the  peduncles  of  the 
cerebellum;  this  is  called  the  fourth  ventricle,  or  ventricle  of 
the  cerebellum.  It  communicates  with  the  third  ventricle  of 
the  cerebrum  by  the  canal  of  Sylvius. 

Isthmus  of  the  encephalon. — This  is  the  term  applied  to 
that  portion  of  the  encephalic  mass  which  unites  the  cerebrum, 
cerebellum,  and  the  spinal  bulb.  It  is  the  point  of  union  of 
the  three  great  divisions  of  the  nervous  centre.  It  comprises 
the  pons  Varolii,  the  peduncles  of  the  cerebrum  and  cere- 
bellum, the  corpora  quadrigemina,  and  the  valve  of  Vieussens. 

At  the  base  of  the  encephalon  there  is  a  convex  projection 
which  surrounds  the  peduncles  of  the  cerebrum  and  cerebel- 
lum like  a  large  ring,  and  which  covers  the  expansions  of  the 
spinal  bulb  toward  these  peduncles  like  a  bridge.  This  is 
the  pons  Varolii,  or  bridge  of  Varolius.  This  projection  is 
the  centre  of  convergence  or  of  emergence  of  the  nervous 
fascicles  or  bundles  which  it  seems  to  cover.  It  is  joined  to 


MEDULLA    OBLONGATA.       SPINAL   CORD.  129 

the  bulb  behind,  and  in  front  to  the  peduncles  of  the  cere- 
brum, and  on  the  sides  to  the  peduncles  of  the  cerebellum. 
Its  inferior  surface,  which  rests  on  the  basilar  apophysis  of 
the  occiput,  shows  fibres  running  transversely.  It  is  grooved 
along  the  median  line,  and  is  perfectly  symmetrical. 

On  its  upper  face  there  are  four  mammillar  projections; 
these  are  the  corpora  quadrigemina.  Behind  these,  and 
between  the  superior  peduncles  of  the  cerebellum,  stretches 
a  thin  layer  of  nerve  substance,  which  has  been  called  the 
valve  of  Vieussens,  and  which  forms  part  of  the  boundaries  of 
the  fourth  ventricle. 

The  bulb  of  the  spinal  cord  or  medulla  oblongata. — This  is 
the  term  applied  to  the  enlargement  of  the  upper  extremity 
of  the  spinal  cord.  Pointing  upward  and  forward,  its  anterior 
surface  corresponds  to  the  basilar  groove  of  the  occiput;  pos- 
teriorly it  rests  in  a  depression  of  the  cerebellum.  Although 
it  is  within  the  cranium,  the  bulb  should  be  studied  at  the 
same  time  as  the  spinal  marrow,  of  which  it  forms  a  part. 

Spinal  cord. — This  name  is  applied  to  the  spinal  portion 
of  the  nervous  centre.  It  is  a  nervous  stem,  white,  cylindrical, 
and  symmetrical,  and  lies  in,  but  does  not  completely  fill,  the 
vertebral  canal;  it  is  held  in  place  by  the  denticulated  ligament 
at  each  side.  It  is  united  with  the  encephalon  by  the  med- 
ulla oblongata.  Terminating  in  a  point  at  its  lower  extremity, 
it  rapidly  increases  in  diameter,  and  forms  the  lumbar  enlarge- 
ment, so  called  from  the  region  which  it  occupies;  in  the 
dorsal  region  it  diminishes  in  size;  augmenting  anew  as  it 
approaches  the  neck,  so  as  to  form  the  cervical  enlargement, 
it  shrinks  again  about  the  middle  of  the  cervical  region,  and 
then  enlarges  a  third  time  at  its  superior  extremity,  and  forms 
the  medulla  oblongata.  The  spinal  marrow  is  marked  in  front 
and  behind,  throughout  its  entire  length,  by  a  fissure  or  median 
furrow,  which  divides  it  into  two  distinct  halves,  excepting  a 
layer  of  white  substance,  which  unites  both  the  two  fissures 
and  the  medullary  fascicles  to  right  and  left.  This  layer, 
sprinkled  with  holes,  designed  to  give  passage  to  vessels,  is 
the  perforated  commissure. 

The  anterior  median  furrow  is  covered  at  the  top  by  the 
interlacing  of  the  nervous  fascicles  which  run  obliquely  from 

9 


130  THE    HUMAN    BODY. 

one-half  of  the  spinal  marrow  to  the  other,  and  of  which  we 
shall  speak  presently.  The  posterior  furrow,  like  the  anterior, 
disappears  insensibly  toward  the  inferior  extremity  of  the 
spinal  cord;  at  its  upper  extremity  it  opens  at  an  acute  angle 
where  the  medulla  oblongata  commences.  Its  form  re- 
sembles the  point  of  a  pen — hence  the  name  calamus  scrip- 
torius  which  has  been  given  to  this  part  of  the  medulla 
oblongata. 

Each  half  of  the  spinal  cord,  separated  from  the  other  by 
the  fissures  indicated  above,  is  composed  of  two  cords  or 
bundles;  one,  the  posterior,  giving  origin  to  the  posterior 
roots  of  the  nerves,  and  the  other,  the  anterior,  to  the 
anterior  roots.  These  cords  are  attached  to,  and  are  con- 
tinuations of,  the  pyramids  of  the  medulla  oblongata. 

This  latter  is  marked  in  front  by  the  median  furrow  which 
extends  beyond  the  interlacing  of  the  fibres,  of  which  men- 
tion has  been  made;  on  each  side  of  this  furrow  there  is 
an  oblong  elevation,  these  are  the  anterior  pyramids ;  outside 
of  which  are  two  projections  still  more  marked,  called  olives 
or  the  olivary  bodies.  Laterally  there  is  a  depression,  grayish 
in  colour,  in  which  terminate  the  posterior  roots  of  the  spinal 
nerves;  behind  this  we  find  a  bundle  of  distinct  fibres,  the 
restiform  or  cord-shaped  bodies ;  and  lastly,  outside  of  these 
bodies  are  fat  posterior  pyramids >  defining  the  calamus  scrip- 
torius  on  either  side.  The  cerebellum,  as  we  have  already 
seen,  covers  the  posterior  surface  of  the  bulb,  to  which  it  is 
united  by  the  restiform  bodies  or  inferior  peduncles  of  the 
cerebellum,  and  which  contribute  with  the  cavity  of  the 
calamus  scriptorius  to  form  the  fourth  ventricle. 

The  anterior  pyramids  terminate  by  the  interlacing  of  their 
nervous  fascicles,  and  this  interlacement  may  be  considered 
as  the  lower  boundary  of  the  medulla  oblongata.  These 
pyramids  are  contracted  at  the  apex  and  at  the  base,  and  are 
inserted  into  the  pons  Varolii  by  a  sort  of  neck  or  contraction. 

The  anterior  and  posterior  roots  of  the  spinal  nerves  form 
two  parallel  lines  on  the  sides  of  the  spinal  marrow.  The 
roots  spring  from  the  spinal  cord,  but  it  cannot  be  ana- 
tomically demonstrated  that  their  fibres  return  to  it  beyond 
the  point  where  they  originate  and  where  they  constitute  by 


MEN1NGES    OR    MEMBRANE    OF   THE    BRAIN.  131 

their  reunion  the  medullary  fascicles.  Opinions  are  not 
fixed  on  the  mode  by  which  union  is  effected  between  the 
nervous  roots  and  the  spinal  cord,  and  we  confine  ourselves 
to  the  simple  statement  that  the  cord  appears  to  consist  of 
a  greater  number  of  nervous  fibres  than  the  nerves  which 
spring  from  it. 

The  isthmus  of  the  encephalon  is  formed  by  the  expansion 
of  the  superior  portion  of  the  spinal  cord;  it  is  the  central 
point  of  the  greater  and  lesser  brain,  of  which  the  hemispheres 
of  the  cerebrum  and  cerebellum  are  but  the  terminal  de- 
velopments. 

Meninges  or  membranes. — The  three  membranes,  placed 
one  above  the  other,  which  line  the  cranium  and  the  vertebral 
canal,  which  envelop  the  encephalon  and  the  spinal  cord, 
and  extend  to  all  their  inequalities,  are  designated  by  this 
term.  They  are  divided  into  the  dura  mater,  the  arachnoid, 
and  the  pia  mater*  The  name  mater,  which  is  given  to  the 
external  and  internal  meninges,  appears  to  have  been  derived 
from  the  Arabs,  who  thus  designated  the  covering  of  any  body 
whatever. 

The  dura  mater  is  a  resistant,  fibrous  membrane,  which 
lines  the  cavity  of  the  skull  and  of  the  spinal  canal.  It 
adheres  very  slightly  to  the  walls  of  this  canal,  but  more 
strongly  to  the  arch  of  the  skull,  and  closely  to  its  base. 
The  arachnoid  and  the  pia  mater  are  interposed  between  the 
dura  mater  and  the  nervous  centre.  It  is  separated  from  the 
spinal  cord  by  a  space  filled  with  the  fluid  peculiar  to  the 
spinal  column ;  but  it  is,  on  the  contrary,  directly  in  contact 
with  the  encephalon,  some  portions  of  which  it  holds  in 
place. 

On  the  median  line  of  the  cranial  arch  is  a  triangular 
canal,  circumscribed  by  the  dura  mater,  called  the  superior 
longitudinal  sinus,  which  performs  the  functions  of  a  large 
vein.  Below  this  sinus  it  forms  a  fold  or  vertical  partition, 
which  is  called  \hzfalx  cerebri  (falx,  a  sickle),  which  descend- 
ing into  the  great  fissure,  separates  the  cerebral  hemispheres. 
In  its  lower  border  is  the  inferior  longitudinal  sinus.  Between 
the  posterior  lobes  of  the  cerebrum  and  the  cerebellum  the 
dura  mater  covers  the  latter  with  the  tentorium  or  tent  of  the 


132  THE    HUMAN    BODY. 

cerebellum,  which  isolates  it  from  the  cerebral  lobes.  It  also 
forms  the  falx  cerebelli,  which  springs  from  the  base  of  the 
skull  between  the  two  hemispheres  of  the  lesser  brain ;  and, 
lastly,  it  extends  beyond  the  cranium,  and  furnishes  the 
covering  of  the  optic  nerve,  and  the  periosteum  of  the  cavity 
of  the  orbit. 

These  folds  and  partitions  formed  by  the  dura  mater 
around  and  between  the  organs  of  the  encephalon,  serve  to 
maintain  the  different  parts  in  place,  to  prevent  their  collision 
'in  shocks  received  on  the  body,  and  to  prevent  the  parts  from 
falling  upon  each  other  in  certain  positions;  as,  for  instance, 
in  lying  on  one  side  the  falx  cerebri  prevents  the  weight 
of  one  hemisphere  from  resting  on  or  compressing  the  other. 
The  disposition  of  the  sinuses  of  the  dura  mater  is  not  less 
remarkable;  they  are,  as  already  stated,  venous  canals  with 
inextensible  walls,  through  which  the  circulation  is  easy,  and 
in  no  danger  from  obstruction  or  suspension ;  and  when  there 
is  an  afflux  of  blood  it  cannot  compress  the  brain,  as  would 
be  the  case  if  the  sinuses  were  replaced  by  veins  with  exten- 
sible walls. 

Arachnoid. — This  membrane  has  been  compared  to  a 
spider's  web  from  its  extreme  tenuity,  and  from  this  it 
derives  its  name.  It  is  a  serous  membrane,  and  lines  the 
dura  mater  throughout  its  whole  extent.  Like  the  other 
serous  membranes,  it  is  a  sac  without  an  opening,  the  walls 
of  which,  placed  back  to  back,  secrete  a  fluid.  It  adheres 
very  strongly,  by  its  external  wall,  to  the  dura  mater,  to  which 
it  moulds  itself,  and  which  it  accompanies  throughout  its 
whole  extent.  Its  internal  wall  is  united  to  the  pia  mater, 
which  separates  it  from  the  nervous  substance  at  many  points. 
This  union  is  so  intimate  that  many  have  thought  the  arach- 
noid has  no  existence  except  where  it  is  detached  from  the 
pia  mater,  as  at  the  level  of  the  fissure  of  Sylvius,  and  in  the 
cerebral  sinuses,  &c.  In  fact,  the  arachnoid  does  not  enter 
those  intervals  where  the  dura  mater  does  not  penetrate,  but 
is  strictly  confined  to  it.  At  these  intervals  there  is  a  cavity 
between  the  serous  membrane  and  the  nervous  centre  which 
it  surrounds,  but  does  not  touch,  as  is  well  illustrated  by  the 
spinal  cord. 


PI  A    MATER.       NERVES.  1 33 

All  the  cavities  formed  by  the  arachnoid  are  filled  with  a 
serous  fluid  called  the  sub-arachnoid  or  cerebro-spinal fluid.  The 
ventricles  of  the  brain  also  contain,  as  has  been  stated,  a 
quantity  of  serous  fluid.  The  use  of  this  fluid  seems  to  be 
to  protect  the  organs  against  the  effect  of  blows  and  shocks. 
The  brain  and  spinal  cord  being,  as  it  were,  suspended  in 
the  arachnoid,  are  held  in  place  in  the  gentlest  possible 
manner  by  the  sub-arachnoid  fluid,  and  by  that  in  the  ven- 
tricles which  moistens  the  surfaces  and  prevents  all  friction. 

Pia  mater. — This  is  the  name  given  to  the  membrane 
which  immediately  surrounds  the  nervous  centre.  It  is  a 
vascular  net-work  of  extreme  delicacy  and  fineness  of  texture, 
and  may  be  considered  as  the  nutritive  membrane  of  the 
cerebro-spinal  organs.  In  its  tissue,  the  arteries  running  to 
the  brain  are  ramified  with  infinite  minuteness,  and  inosculate 
with  the  radicles  of  the  veins  which  spring  from  it.  It 
follows  closely  all  the  cerebral  convolutions;  penetrates  the 
furrows,  and  into  the  ventricles,  and  covers  even  the  thin 
layers  of  the  cerebellum.  It  becomes  denser  and  more 
fibrous  around  the  spinal  cord,  of  which  it  forms  the  neuri- 
lemma  or  envelope,  as  well  as  at  the  origin  of  the  nerves. 

To  recapitulate,  the  greater  and  lesser  brain,  and  the  spinal 
cord,  contained  in  the  skull  and  spinal  canal  inclosed  in 
three  superposed  membranes,  are  united  by  a  common 
centre,  the  isthmus  of  the  encephalon.  Nerves  spring  from 
the  brain  and  spinal  cord. 

Nerves. — This  is  the  name  given  to  white  or  grayish  threads 
which  are  attached  by  one  extremity  to  the  cerebro-spinal 
nervous  centre,  and  at  the  other  are  distributed  to  the  organs. 
The  nerves  are  composed  of  very  fine  filaments,  united  at 
the  point  at  which  they  spring  from  the  nervous  centre  in 
bundles  called  the  roots  of  the  nerves;  these  roots  unite  and 
form  the  trunks  which  ramify  and  disappear,  as  it  were,  in 
the  tissues  of  the  body.  A  sheath  of  cellular  tissue  called 
neurilemma  or  perineurium,  envelops  the  nerves,  and  pene- 
trates between  the  fibres  formed  by  the  union  of  the  nerve- 
tubes  spoken  of  in  treating  of  the  tissues.  The  ramifications 
of  the  nerves  unite  and  seem  to  be  confounded  at  certain 
points  where  they  form  a  very  complicated  net-work,  which  is 


134  THE   HUMAN    BODY. 

termed  a  plexus;  but  this  union  is  effected  solely  by  the 
neurilemma.  One  nerve-fibre — properly  speaking — never  is 
confounded  with  another.  It  runs  without  interruption,  and 
always  distinct,  through  the  most  intricate  net-work,  from  the 
nervous  centre  to  the  organ  which  it  serves.  From  the 
analogy  with  the  union  of  the  blood-vessels,  we  speak  of  the 
anastomosis  of  the  nerves,  and  we  shall  soon  see  that  if  the 
union  of  the  vessels  with  each  other  is  an  essential  condition 
of  the  circulation  of  the  blood,  the  distinct  and  absolute  in- 
dependence of  the  nerves,  even  to  their  minutest  ramifica- 
tions, is  no  less  necessary  to  the  integrity  of  the  nervous 
functions.  We  may  therefore  compare  the  union  of  the 
nerves  by  juxtaposition  during  their  course  to  a  bundle  of 
electric  wires  which,  though  united,  are  always  distinct, 
because  of  their  isolating  covering.  The  isolating  covering 
of  the  nerves  is  the  neurilemma. 

M.  Sappey  has  recently  described,  under  the  name  of  the 
nervi  nervornm,  or  nerves  of  the  nerves,  the  filaments  which 
run  to  the  neurilemma,  and  which  stand  in  precisely  the 
same  relation  to  the  nerves  that  the  nerves  themselves  do 
to  the  entire  organism. 

There  are  two  orders  of  nerves:  the  one,  under  the  influ- 
ence of  the  will,  causes  motion  in  the  organs ;  these  are  the 
nerves  of  animal  life:  the  other  presides  over  the  functions  of 
the  viscera  without  our  consciousness,  and  without  any  effort 
of  will;  these  are  the  nerves  of  organic  life.  The  first  are 
cranial  or  spinal  nerves,  and  spring  directly  from  the  nervous 
centres,  they  are  white  and  generally  of  a  resistant  texture; 
the  second,  ganglionic  or  visceral  nerves,  although  connected 
with  the  nervous  centre,  form  a  system  apart,  which  is  called 
the  great  sympathetic.  These  nerves  are  for  the  most  part 
soft,  and  of  a  grayish  colour. 

Cranial  and  spinal  nerves. — These  nerves  are  all  disposed 
in  twos,  and  form  a  series  of  pairs  to  the  number  of  forty, 
of  which  nine  pairs  are  cranial  or  cerebral,  and  thirty-one 
pairs  are  spinal. 

The  cranial  nerves  are  classed  as  follows : — 

ist  pair.  Olfactory  nerves,  which  are  ramified  in  the 
organ  of  smell. 


ENUMERATION    OP   CRANIAL   NERVES.  135 

2d  pair.  Optic  nerves,  which  preside  over  the  organs  of 
sight.  Its  terminal  expansion  forms  the  retina. 

3d  pair.  The  common  oculo-motor  nerves,  which  are  dis- 
tributed to  most  of  the  muscles  which  move  the  eyeball. 

4th  pair.  Pathetic  nerves,  so  called,  because  they  give  the 
power  of  motion  to  the  great  oblique  muscle,  the  action  of 
which,  upon  the  eyeball,  is  one  of  the  principal  elements  in 
the  expression  of  the  face. 

5th  pair.  The  trigeminal  or  trifacial  nerve  forms  on 
either  side  three  nerves,  the  ophthalmic  and  the  superior 
and  inferior  maxillary;  they  are  distributed  over  the  face, 
and  to  the  organs  which  constitute  it. 

6th  pair.  The  external  oculo-motor  nerves.  These  go  to 
the  external  straight  muscle  of  each  eyeball.  The 

yth  pair  is  divided  into  the  hard  portion  or  facial  nerve, 
which  goes  to  the  face,  and  the  soft  portion  or  auditory  nerve, 
which  goes  to  the  internal  ear.  The 

8th  pair  is  divided  into  three  branches:  i.  the  glosso-pha- 
ryngeal,  the  nerve  of  taste,  running  to* the  tongue  and  pharynx, 
and  furnishing  branches  to  several  muscles  of  the  neck,  to  the 
tonsils,  &c.  2.  The  pneumo-gastric  nerve,  which  branches 
out  to  the  cervical  region,  to  the  pharynx,  the  larynx,  the 
lungs,  and  the  stomach.  3.  The  spinal  accessory  of  Willis, 
which  sends  branches  to  several  muscles  of  the  neck,  to  the 
pharynx,  and  to  the  larynx. 

9th  pair.  The  great  hypoglossal  nerves,  which  give  move- 
ment to  the  tongue. 

The  spinal  nerves  form  eight  cervical  pairs,  twelve  dorsal, 
five  lumbar,  and  six  sacral.  They  all  spring  from  the  spinal 
cord  in  two  bundles  of  roots,  called  the  anterior  and  posterior 
roots,  according  to  the  portion  of  the  cord  from  which  they 
emerge.  These  roots  are  enveloped  in  a  membranous  sheath, 
and  unite  to  form  the  trunk  of  the  nerve  at  a  point  more  or 
less  distant  from  their  origin,  according  to  the  region  from 
which  they  proceed.  The  roots  of  the  lumbar  and  sacral 
nerves  form  a  bundle  of  independent  cords  in  the  inferior 
portion  of  the  spinal  canal,  which,  from  their  peculiar  dis- 
position, has  been  named  the  cauda  equina  or  horse-tail. 

On  a  level  with  the  openings  through  which  the  nerves 


136  THE    HUMAN    BODY. 

pass  from  the  spinal  canal,  the  posterior  roots  form  a  ganglion 
on  each  side  to  which  the  anterior  roots  unite  themselves, 
and  from  which  the  nerve  is  distributed  to  the  organism,  by 
three  classes  of  spinal  branches,  anterior ',  posterior •,  and  gan- 
glionic;  the  latter  unite  with  the  great  sympathetic. 

The  first  four  pairs  of  cervical  nerves  form  by  the  con- 
tiguity of  their  branches  the  cervical  plexus ;  the  ramifications 
of  which  distribute  themselves  to  the  surface,  and  to  the 
deep  portions  of  the  neck,  to  the  outside  of  the  head,  to  the 
shoulder,  and  to  the  upper  portion  of  the  back. 

The  last  four  pairs  constitute  the  brachial  plexus,  which, 
after  furnishing  numerous  branches  to  the  shoulder  and  back, 
go  to  the  arm  as  the  brachio-cutaneous,  musculo-cutaneous, 
median,  radial,  and  ulnar  nerves. 

The  twelve  pairs  of  dorsal  or  intercostal  nerves,  as  well  as 
the  five  pairs  of  lumbar  nerves,  are  ramified  in  the  walls  of 
the  thorax  and  abdomen,  and  in  the  muscles  of  the  back  and 
loins.  The  lumbar  plexus  furnishes,  among  other  principal 
branches,  the  crural  nerve,  which  ramifies  into  the  musculo- 
cutaneous  of  the  leg,  and  the  external  and  internal  saphenous 
nerves,  &c. 

The  six  pairs  of  sacral  nerves  are  distributed  to  the  pelvis 
and  to  the  lower  limbs.  The  first  four  pairs  with  the  last 
lumbar  pair  form  the  sacral  plexus,  the  principal  terminal 
branch  of  which  is  the  sciatic  nerve.  This  is  the  largest 
nerve  in  the  body;  it  descends  through  the  posterior  portion 
of  the  thigh,  to  the  muscles  of  which  it  furnishes  several 
branches;  and  a  little  above  the  knee  it  divides  into  two 
trunks — the  internal  popliteal  we  tibial,  and  the  external  or 
peroneal,  which  distribute  themselves  by  numerous  ramifica- 
tions to  the  muscles  of  the  leg  and  foot. 

The  great  sympathetic. — The  nervous  apparatus  designated 
by  this  name  consists  of  a  double  cord  placed  on  either  side 
of  the  spinal  column,  the  whole  length  of  the  neck,  and  in 
the  interior  of  the  thoracic  and  abdominal  cavities.  It  is,  as 
has  ajready  been  stated,  the  nervous  system  of  organic,  vege- 
tative, or  nutritive  life.  Extending  from  the  first  cervical 
vertebra  to  the  last  vertebra  of  the  sacrum,  the  great  sym- 
pathetic enlarges  at  the  level  of  each  vertebra,  and  forms 


FUNCTIONS    OF    THE    NERVOUS    SYSTEM.  137 

nervous  ganglia,  which  communicate  by  external  filaments  with 
all  the  cranial  or  spinal  pairs,  and  constitute  by  their  internal 
filaments  all  the  visceral  nerves.  This  string  of  ganglia  gives 
the  great  sympathetic  the  name  of  the  ganglionic  nervous 
system. 

The  great  sympathetic  forms  the  pharyngeal,  the  cardiac, 
the  solar  or  coiliac  and  the  hypogastric  plexuses.  These  are 
the  nervous  centres  of  organic  life. 

The  nerves  emanating  from  the  great  sympathetic  surround 
the  arteries  like  a  sheath,  and  penetrate  with  them  into  the 
organs.  Some  of  these  nerves,  as  has  already  been  stated, 
are  soft  and  of  a  grayish  colour,  and  others  are  white  and 
firm. 

Functions  of  the  nervous  system. — The  nervous  system  is 
the  seat  of  intelligence,  of  sensation,  and  of  motion;  it  is  the 
centre  of  action  for  the  organism,  and  it  presides  over  all  the 
phenomena  which  together  constitute  life.  Its  spinal  and 
superficial  portions — the  cord  and  the  nerves — take  part  only 
in  the  functions  of  sensation,  of  motion,  and  of  organic  life: 
but  the  encephalon  contributes  at  once  to  the  material  and 
mental  functions. 

Observers  have  succeeded  in  distinguishing  in  the  nerves 
and  spinal  cord  the  apparatus  which  is  specially  devoted  to 
sensation,  from  that  which  presides  over  motion.  But  the 
knowledge  which  we  have  attained  concerning  the  special 
functions  of  the  different  parts  of  the  encephalon  is  as  yet 
very  limited,  and  for  the  most  part  hypothetical.  Compara- 
tive physiology  teaches  us  that  some  portions  are  extremely 
sensitive  and  irritable,  while  others  are  not  affected  by- 
external  agents.  The  medulla  oblongata,  the  pons  Varolii, 
and  quadrigeminal  bodies,  are  most  allied  to  the  spinal  cord, 
and  anatomy  can  follow  thither  the  medullary  fascicles  en- 
dowed with  sensibility,  but  beyond  them  these  same  fascicles 
become  insensible  in  the  greater  and  lesser  brain,  the  optic 
beds,  &c.  It  appears  that  after  having  transmitted  the  external 
impression,  they  change  their  nature,  becoming  an  integral 
portion  of  the  organ  in  which  the  sensation  is  produced,  and 
submitted  to  the  apprehension  of  the  intelligence.  We  are 
no  less  embarrassed  if  we  attempt  to  specify  the  portions  of 


138  THE    HUMAN    BODY. 

the  encephalon  which  preside  over  motion.  As  for  the  seat 
of  the  intellectual  faculties,  we  cannot  doubt  that  it  is 
situated  in  the  encephalon,  but  science  possesses  no  exact 
data  regarding  the  part  played  by  the  different  organs  con- 
tained in  the  cranial  cavity  in  the  elaboration  of  thought, 
and  the  soul  cannot  perceive  the  mysterious  tie  which  unites 
it  with  these  organs. 

The  nervous  system,  which  gives  motion  and  sensibility  to 
every  part  of  the  body,  is  itself  absolutely  dependent  on  the 
circulation.  It  determines '  and  regulates  its  progress  by 
exciting  the  action  of  the  heart,  but  it  must  itself  be  excited 
by  the  afflux  of  blood  which  the  arteries  bring  to  it;  and  just 
as  the  heart  slackens  or  even  stops  its  action  under  the  in- 
fluence of  certain  impressions,  the  functions  of  the  brain, 
spinal  cord,  and  nerves  are  inevitably  suspended  when  the 
blood  does  not  come  to  awaken  the  nervous  energy.  Any 
impediment  to  circulation  of  the  blood  induces  paralysis, 
more  or  less  complete,  in  the  parts  beyond  the  obstacle,  and 
no  sooner  does  the  nourishing  fluid  stop  its  motion,  or  even 
slacken,  in.  its  course  toward  the  brain,  than  syncope  or 
fainting  supervenes;  that  is  to  say,  the  functions  of  the 
encephalon  are  weakened  or  cease  altogether. 

In  giving  a  summary  description  of  the  nervous  system, 
we  have  proceeded  from  centre  to  circumference,  but  in 
describing  the  nervous  functions  the  reverse  course  seems 
preferable. 

Functions  of  the  sensitive  and  motor  spinal  nerves. — Sensa- 
tion may  be  destroyed  in  a  portion  of  the  body  while  it  still 
possesses  the  power  of  motion,  and  conversely  a  limb  may 
lose  the  power  of  motion  and  still  remain  sensitive  to  ex- 
ternal impressions.  This  independence  of  motion  and  of 
sensation  revealed  to  the  physiologists  of  antiquity  the  exist- 
ence of  two  orders  of  nerves,  one  sensitive  the  other  motor. 
Boerhaave  and  other  modern  anatomists  accepted  these 
doctrines,  on  which  Lamarck  based  and  promulgated  theories 
nearly  approaching  the  truth;  but  Sir  Charles  Bell  was  the 
first  to  distinguish,  by  actual  experiment,  the  nerves  of 
sensation  from  those  of  motion,  and  to  show  that  they  sprang 
from  two  distinct  portions  of  the  spinal  cord. 


FUNCTIONS    OF    SPINAL    NERVES.  139 

The  anterior  fascicles  of  the  cord  and  the  anterior  roots 
of  the  nerves  which  proceed  from  them  are  insensible,  and 
produce  muscular  contraction.  The  posterior  fascicles  of  the 
cord,  and  the  posterior  roots  of  the  nerves,  have  no  motor 
power,  but  they  are  sensitive.  Each  spinal  nerve,  formed  by 
the  union  of  the  anterior  and  posterior  roots,  contains  sensi- 
tive filaments  and  motor  filaments  placed  side  by  side  in  its 
trunk  and  its  ramifications.  It  follows,  therefore,  that  these 
nerves  and  their  subdivisions  are  mixed;  as  regards  the 
composition  of  their  fascicles,  they  are  at  once  sensitive  and 
motor.  They  are  sensitive  to  mechanical  irritation,  and  they 
excite  muscular  contraction  under  the  influence  of  galvanism, 
for  both  these  agents  meet  in  the  same  nerve-filaments 
subject  to  their  power.  These  filaments,  separately  con- 
sidered, come  from  the  centre  to  the  periphery  without 
division  and  without  anastomosing,  in  the  exact  sense  of  the 
word,  for  what  is  called  anastomosis  of  the  nerves  is  a  simple 
juxtaposition,  proximity  without  exchange  of  their  proper 
substance,  and  without  intimate  fusion. 

It  is  to  the  continuity  of  the  nervous  filaments,  and  to  their 
independence,  that  distinctness  of  tactile  sensation  and  pre- 
cision of  motion  is  due.  It  is  clear,  therefore,  that  if  two 
sensitive  filaments  should  unite  their  proper  substance,  the 
impressions  perceived  by  them  previous  to  their  union  would 
be  confounded,  and  would  not  be  referred  by  the  brain  to 
distinct  points.  If,  for  example,  two  filaments  running  to 
the  index  and  middle  fingers,  were  united,  instead  of  being 
simply  placed  side  by  side,  at  any  point  between  the  finger- 
tips and  the  brain,  they  would  carry  to  the  brain  but  one 
single  sensation  for  both  fingers,  and  it  would  be  impossible 
to  tell  upon  which  one  the  impression  had  been  made.  The 
result  would  be  the  same  if  two  filaments  of  a  motor  nerve 
running  to  these  fingers  were  united,  instead  of  isolated  in 
their  proper  substance;  the  motor  impulse  would  be  trans- 
mitted to  both  fingers  alike,  and  the  brain  could  not  move 
either  expressly. 

In  persons  who  have  suffered  amputation,  phenomena  are 
produced  which  are  explained  by  the  fact  that  all  the  fila- 
ments of  a  nerve  exist  at  its  origin  which  are  found  at  its 


140  THE    HUMAN    BODY. 

extremity.  The  man  who  has  lost  an  arm  or  a  leg,  feels 
pains,  which  he  refers  not  to  the  stump  which  remains,  but 
to  the  hand  or  the  foot  which  he  has  lost.  It  is  the  nervous 
filaments  primitively  destined  to  these  parts  which  are  the 
seat  of  the  pain,  and  which  now  transmit  it  as  coming  from 
the  organ  to  which  they  formerly  gave  sensibility.  The  same 
effect  is  produced  when  a  piece  of  skin  has  been  transplanted 
from  the  forehead  to  the  nose  by  autoplasty;  if  the  patient 
be  touched  on  the  nose  he  feels  the  impression  on  his  fore- 
head. 

We  shall  see  in  treating  of  the  senses,  that  tactile  impres- 
sions may  be  distinct  on  the  tips  of  the  fingers,  at  a  distance 
of  one-fiftieth  of  an  inch  from  each  other;  which  implies  that 
there  are  two  filaments  at  this  interval  from  each  other,  running 
directly  to  the  brain,  but  we  err  if  we  reckon  in  this  way  the 
extent  of  nerve  subdivision,  for  every  point  in  the  skin,  how- 
ever small,  is  sensitive  to  the  touch.  It  is  by  innumerable 
ramifications,  each  of  which  contains  at  least  one  nervous 
filament,  that  the  nerves  terminate  in  the  organs,  those  of 
motion  to  excite  muscular  contraction,  and  those  of  sensa- 
tion to  receive  and  transmit  impressions. 

Functions  of  the  cranial  nerves. — Like  those  which  spring 
from  the  spinal  cord,  the  nerves  of  the  brain  are  divisible 
into  motor  and  sensory  nerves.  Among  these  last  some  are 
endowed  with  a  special  sensibility,  as  the  olfactory,  the  optic, 
and  auditory  nerves;  the  others  transmit  general  sensations. 
Several  of  the  cranial  nerves  are  made  up  of  filaments  of 
different  orders,  and  are  formed  by  the  union  of  nerves  of 
general  sensation,  of  special  sensation,  or  of  motion.  Like 
the  spinal  nerves  after  the  union  of  their  roots,  they  form 
cords,  mixed  in  their  functions  as  a  whole,  but  distinct  in 
those  of  their  several  filaments.  The  analogy  between  the 
cranial  and  the  spinal  nerves  is  completed  by  the  branches 
which  go  from  the  cranial  nerves  of  sensation  to  the  great 
sympathetic,  and  by  the  gray  fibres  which  are  seen  near  the 
origin  of  the  cranial  nerves,  and  also  near  the  posterior  roots 
of  the  spinal  nerves.  In  the  cranium  the  motor  nerves 
emerge  from  the  prolongation  of  the  anterior  fascicles  of 
the  cord  in  which  the  spinal  motor  nerves  originate, 


FUNCTIONS    OF    SPINAL    CORD.       ENCEPHALON.  141 

Functions  of  the  spinal  cord. — We  have  already  seen  that 
the  anterior  fascicles  of  the  spinal  cord  are  insensitive,  and 
that  they  give  motor  power  to  the  anterior  roots  of  the  nerve, 
while  the  posterior  portions  are  sensitive,  like  the  nerves 
which  emerge  from  them.  These  properties  of  the  medul- 
lary fascicles  were  for  a  long  period  disputed,  but  they  have 
been  clearly  demonstrated  by  M.  Longet's  experiments. 
The  spinal  cord  imparts  to  the  nerves  of  the  trunk  and  limbs 
the  power  of  voluntary  and  respiratory  motion.  It  is  also 
the  source  of  nervous  energy  in  the  action  of  the  heart,  and 
in  the  circulation  of  the  blood,  in  the  phenomena  of  nutrition 
and  of  secretion;  lastly,  it  seems  to  have  only  an  indirect  in- 
fluence on  the  production  and  maintenance  of  animal  heat. 
When  there  is  any  lesion  of  one  of  the  lateral  halves  of  the 
cord,  it  is  on  the  corresponding  side  of  the  body  that  motion 
and  sensation  are  disturbed  or  destroyed.  The  action 
therefore  of  the  spinal  cord  is  direct  on  the  organs  to  which 
it  sends  nerves,  and  not  crossed  like  that  of  the  encephalon. 

Functions  of  the  encephalon.  Medulla  oblongata. — The  me- 
dulla is  the  central  source  and  regulator  of  the  respiratory 
movements.  It  is  in  a  limited  portion  of  this  enlargement 
of  the  cord,  near  the  origin  of  the  eighth  pair  of  nerves,  that, 
as  Flourens  has  demonstrated,  the  organ  which  he  calls  the 
prime  mover,  or  vital  node,  of  the  respiratory  mechanism  has 
its  seat.  This  organ,  according  to  M.  Longet,  does  not 
comprise  all  the  substance  of  the  bulb,  but  is  only  a  fascicle, 
composed  of  gray  substance  between  the  pyramidal  and 
restiform  bodies.  The  medulla  transmits  impressions  from 
the  cord  to  the  brain,  and  the  impulse  of  the  will  from  the 
brain  to  the  cord;  its  anterior  and  posterior  portions  are 
prolongations  of  the  corresponding  medullary  fascicles,  and 
we  may  conclude  therefore  that  they  share  their  functions  as 
they  do  their  substance;  and  that  the  medulla  by  its  ante- 
rior portion  controls  movement,  and  by  its  posterior  portion 
sensation.  In  point  of  fact,  all  the  nerves  which  spring  from 
the  anterior  portion  are  sensitive,  and  from  the  posterior 
motor.  The  anterior  fascicles  of  the  medulla  cross  their 
fibres,  and  from  this  results  a  cross  action  on  the  motor 
nerves,  which  originate  from  these  fascicles;  the  posterior 


142  THE    HUMAN    BODY. 

fascicles,  on  the  contrary,  do  not  cross  each  other,  and  their 
action  is  direct. 

Pons  Frtn?///.— -The  movements  of  locomotion  are  origi- 
nated specially,  according  to  M.  Longet,  in  the  pons  Varolii. 
This  portion  of  the  encephalon  has  a  cross  action  on  motion. 
It  is  a  centre  of  perception  for  tactile  sensations,  but  nothing 
authorizes  us  to  believe  that  it  can  appreciate  sensation  by 
itself  alone,  and  without  the  aid  of  the  cerebral  lobes. 

Peduncles  of  the  brain. — These  organs  unite  the  greater 
and  lesser  brain  to  the  isthmus  of  the  encephalon,  and  to  the 
spinal  cord,  and  seem  to  be  solely  devoted  to  the  transmis- 
sion of  motion  and  sensation.  An  injury  to  one  of  the 
middle  peduncles  of  the  cerebellum  causes  the  body  to  turn 
on  its  axis;  a  phenomenon  which  has  been  variously  explained 
by  different  writers. 

Corpora  quadrigemina,  or  quadrigeminal  bodies. — These 
bodies  take  an  essential  part  in  vision,  either  by  inducing 
the  contractions  of  the  iris,  or  in  contributing  to  visual  per- 
ceptions. 

Pineal  gland. — The  hypothesis  of  Descartes  has  popular- 
ized, so  to  speak,  this  organ,  whose  functions  are  entirely 
unknown.  The  illustrious  philosopher  believes  the  pineal 
gland  to  be  "the  source  from  whence  the  most  subtle  parts  of 
the  blood,  the  spirits,  flow  to  all  parts  in  the  brain,  and  are 
directed  to  a  particular  point,  according  as  the  gland  is  in- 
clined one  way  or  the  other."  This  idea  of  Descartes  has 
been  parodied,  by  making  the  pineal  gland  the  seat  of  the 
soul,  from  whence  it  directs  the  impulses  of  the  brain  by  two 
nervous  prolongations,  called  the  "  reins  of  the  mind " 
(habena  animi). 

The  optic  beds. — In  spite  of  the  name  which  has  been  given 
them,  these  portions  of  the  encephalon  do  not  seem  to  have 
any  appreciable  action  on  the  sense  of  vision;  but  they  act 
upon  the  voluntary  movements  in  such  a  manner  that  the 
influence  of  the  right  half  is  felt  on  the  left,  and  vice  versa; 
this  is  called  cross  action,  which  is  caused,  as  already  stated, 
by  the  crossing  of  the  cerebral  fibres.  The  optic  beds  seem 
to  have  no  influence  over  the  movements  of  the  upper 
extremities,  as  has  been  thought  by  several  physiologists. 


FUNCTIONS    OF    CEREBRUM.  143 

It  is  unnecessary  to  enumerate  the  other  portions  of  the 
encephalon,  of  which  the  functions  are  doubtful,  or  entirely 
unknown. 

Cerebrum. — Observation  has  enabled  physiologists  to  dis- 
tinguish in  the  spinal  cord  and  spinal  nerves,  and  even  in  the 
cranial  nerves,  the  sensitive  and  motor  portions;  and  we  must 
admit  from  the  results  of  experiment  in  comparative  ana- 
tomy, that  certain  regions  of  the  encephalon  are  endowed 
with  sensibility,  while  others  are  insensible;  but  we  have  not 
yet  been  able  to  recognize  in  the  encephalic  mass  the  central 
organs,  which  preside  over  sensation  and  over  motion.  No- 
thing authorizes  us  to  think  that  the  insensible  portions  of 
the  brain  do  not  take  a  part  in  the  motor  and  sensatory 
functions,  and  we  are  still  less  able  to  point  out  in  the  en- 
cephalon the  seat  of  intelligence.  We  see  the  intellectual 
faculties  develop  themselves  in  the  child,  at  the  same  time 
with,  and  in  proportion  to,  the  development  of  the  brain; 
and  we  know  that  these  faculties  continue  imperfect,  or 
changed,  when  the  normal  development  of  the  organ  is 
arrested,  and  when  it  suffers  from  certain  lesions;  but  these 
facts,  incontestable  in  principle,  have  no  absolute  applica- 
tion. The  brain  may  be  wounded,  and  even  a  portion  of  it 
may  be  destroyed,  without  any  sensible  change  in  the  intel- 
lectual faculties;  a  man  of  genius  may  have  an  ill-developed 
brain,  as  Bichat,  for  example,  whose  cerebral  lobes  were  not 
of  equal  volume.  On  the  other  hand  we  see  the  intellect 
clouded  under  the  influence  of  alcohol,  of  certain  poisonous 
substances,  or  an  attack  of  fever,  and  no  trace  is  left  in  the 
encephalon  of  the  temporary  disturbance ;  sleep  produces  an 
analogous  effect;  dreams  are  only  a  succession  of  false  ideas, 
a  real  delirium  which  ceases  on  awaking.  And,  indeed,  in 
the  insane,  science  can  in  many  cases  prove  nothing  but  their 
misfortune,  of  which  no  part  of  the  brain  suggests  in  the 
slightest  degree  the  organic  cause.  Physiology,  therefore,  is 
very  reserved  in  regard  to  the  cerebral  functions,  and  most 
of  its  theories  concerning  them  are  disputed  and  uncertain. 

The  cerebral  lobes  do  not  seem  to  be  essentially  necessary 
to  the  perception  of  sensitive  impressions,  general  or  special. 
Thus,  pathological  observation  has  established  the  fact,  that 


144  THE   HUMAN    BODY. 

vision  may  be  equally  good  in  both  eyes,  although  one  hemi- 
sphere may  be  atrophied,  or  may  have  suffered,  as  from 
wounds,  a  great  loss  of  substance.  It  is,  on  the  contrary, 
exclusively  in  the  cerebral  lobes  that  the  perception  of  sen- 
sations lies,  and  that  the  ideas  are  formed  which  these  sensa- 
tions create.  It  is  also  from  the  hemispheres  that  the  im- 
pulse emanates,  which  results  in  voluntary  motion.  Some 
physiologists  have  referred  this  impulsion  to  the  white,  and 
others  to  the  gray  substance  of  the  brain.  Wherever  may 
be  the  seat  of  the  motor  principle,  we  know  that  the  brain 
exercises  a  cross  action  on  the  muscles;  that  is,  the  left  hemi- 
sphere induces  the  movements  of  the  right  side,  and  the 
right  hemisphere  those  of  the  left.  But  in  certain  cases  the 
action  is  direct  notwithstanding;  this  has  been  explained  by 
an  exceptional  incompleteness  of  the  crossing  of  the  cerebral 
fibres.  Physiologists  have  sought  in  vain  to  localize  the 
source  of  motion  in  the  brain,  and  the  difference  of  opinion 
on  this  point  does  not  permit  us  to  consider  it  a  settled 
question. 

The  encephalon  controls  the  intellectual  phenomena,  and 
most  authors  consider  the  cerebral  lobes  the  seat  of  the  soul. 
In  the  superior  animals  the  most  complete  development  of 
the  brain  proper  coincides,  in  fact,  with  the  greatest  degree 
of  intelligence,  and  the  proportions  of  the  brain  of  man 
unite  with  his  intellect  in  placing  an  immense  interval  between 
him  and  animals  the  most  gifted  in  this  respect.  And  lastly, 
the  encephalon  in  idiots  is  specially  characterized  by  atrophy 
of  the  cerebral  lobes,  of  their  convolutions,  and  of  the  gray 
or  cortical  substance.  Several  authors,  from  repeated  observa- 
tion of  this  latter  fact,  have  considered  the  gray  substance 
as  the  seat  of  the  intellectual  faculties. 

We  have  already  stated,  in  speaking  of  the  skull,  that  Gall 
and  his  school  have  placed  the  intellectual  faculties  in  the 
anterior  lobes  of  the  brain,  the  moral  qualities  or  tendencies 
of  the  mind  in  the  middle  lobes,  and  the  animal  faculties  or 
instinctive  propensities  in  the  posterior  lobes.  This  doctrine 
seems  to  be  the  rational  consequence  of  that  which  recog- 
nizes one  portion  of  the  encephalon  as  specially  designed  for 
the  functions  of  the  intellect;  but  if  we  admit  the  possible 


FUNCTIONS    OF   GREAT    SYMPATHETIC.  145 

existence  in  the  brain  of  distinct  and  multiplied  apparatus  in 
the  explanation  of  psychological  phenomena,  it  is  simply  a 
hypothesis  of  which  it  is  out  of  our  power  to  furnish  a  single 
proof.  It  is  objected,  and  with  reason,  to  the  phrenological 
theory,  that  it  groups  all  the  faculties  in  those  portions  of 
the  brain  which  correspond  to  the  arch  of  the  skull,  to  the 
exclusion  of  those  resting  on  its  base;  and  besides,  patho- 
logical anatomy  is  not  in  accord  with  the  theory  of  Gall,  and 
comparative  anatomy  does  not  permit  its  admission. 

The  cerebellum. — Among  the  various  functions  which  physi- 
ologists have  attributed  to  the  cerebellum,  one  only  has  been 
generally  admitted  in  latter  times;  that  is  the  co-ordination 
of  movement.  The  repeated  experiments  of  Flourens,  con- 
firmed by  those  of  MM.  Bouillaud  and  Longet,  seem  to 
prove  that  the  injury  or  absence  of  the  cerebellum  causes  a 
confusion  in  the  movements  similar  to  that  induced  by  intoxi- 
cation, and  that  this  organ  is,  in  fact,  the  regulator  of  motion. 
Still  pathological  anatomy  does  not  agree  in  this  respect  with 
the  experiments  made  upon  animals.  Perfect  integrity  of 
function,  and  especially  of  locomotion,  has  been  observed  in 
congenital  absence  of  the  cerebellum.  A  great  number  of 
observations  made  by  M.  Andral  prove  that  the  cerebellum 
may  be  diseased  while  movements  do  not  cease  to  be  co- 
ordinated. The  recent  investigations  of  M.  Duchenne,  of 
Boulogne,  also  contradict  the  theory  of  Flourens,  and  it  is 
now  perfectly  well  known  that  the  greatest  disorder  may 
exist  in  the  movements  without  the  slightest  indication  of 
lesion  in  the  cerebellum. 

Functions  of  the  great  sympathetic. — The  nervous  apparatus 
designated  by  this  name  is  formed,  as  we  know,  by  the  sensi- 
tive and  motor  filaments  coming  from  the  cranial  nerves,  or 
from  the  roots  of  the  spinal  nerves.  That  is,  its  ramifications 
are,  at  the  same  time,  sensitive  and  motor.  The  movements 
excited  by  the  great  sympathetic  are  not  under  the  influence 
of  the  will.  The  motor  impulse  springing  from  this  system 
differs  also  from  that  which  determines  voluntary  movements, 
in  that  it  travels  less  rapidly.  Experiments  upon  animals 
also  prove  that  the  ganglia  and  ramifications  of  the  great 
sympathetic  continue  their  functions  some  time  after  they 

10 


146  THE    HUMAN    BODY. 

cease  to  be  in  communication  with  the  nervous  centre. 
The  movements  they  induce  are  then  executed  under  the 
influence  of  the  nervous  force  pre-existing,  and  stored  up  irr 
their  substance.  The  great  sympathetic  gives  motion  and 
sensation  to  the  machinery  of  organic  life;  it  controls  the 
nutritive  functions,  the  circulation,  the  secretions,  &c. 

Reflex  power.  —  Besides  the  voluntary  movements  which 
result  from  the  transmission  of  impressions  by  the  nerves  of 
sensation,  and  from  the  perception  of  these  impressions, 
others  are  produced  in  which  the  will  has  no  part,  and  which 
result  from  the  impulse  directly  reflected  upon  the  motor  nerves, 
without  any  sensation  having  necessarily  taken  place,  or  at 
least  without  our  having  any  consciousness  of  it.  These 
are  called  reflex  movements,  and  the  force  which  determines 
them,  and  is  considered  as  peculiar  to  the  nervous  centre,  is 
called  reflex  power  or  the  excito-motor  faculty.  Several  physi- 
ologists have  considered  the  phenomena  classed  under  the 
name  of  recurrent  sensibility  as  belonging  to  this  reflex  action, 
but  upon  the  origin  of  this  sensibility  authors  are  not  agreed. 

Lastly,  there  is  another  reflex  action  which  gives  rise  to 
sympathy,  that  is  the  particular  influence  which  certain  organs 
exercise  upon  others,  such  as  the  sensation  called  setting  the 
teeth  on  edge,  produced  by  the  grinding  of  metal  against 
stone  or  glass,  and  the  sneezing  provoked  by  tickling  the 
pituitary  membrane,  or  by  snuff,  &c.  (See  Movements,  p.  59.) 

Nervous  force. — The  almost  instantaneous  transmission  of 
sensation  and  the  motor  impulse,  by  the  different  parts  of 
the  nervous  system,  is  one  of  the  mysteries  of  the  organism. 
This  class  of  phenomena  has  been  compared  to  those  pro- 
duced in  nature  by  electricity  or  magnetism,  and  the  ques- 
tion has  been  raised  whether  the  nervous  system  is  not 
under  the  influence  of  an  imponderable  fluid  produced  in 
its  substance,  or  drawn  from  the  same  source  as  all  the 
elements  of  animate  matter.  Various  names,  such  as  nervous 
fluid,  nervous  force,  the  active  principle  of  the  nerves,  have 
been  given  to  the  agent  whose  hypothetical  existence  permits 
us  to  explain  the  nervous  functions,  as  we  explain  the  action 
of  the  galvanic  pile  or  the  movements  of  the  magnetic 
needle.  The  admirable  discovery  of  Galvani  seemed  to 


NERVOUS    FORCE.      MEMORY.  147 

prove  the  analogy,  if  not  the  identity,  of  the  electric  and 
nervous  fluids.  Naturalists  and  physicians  have  striven  to 
establish  by  the  aid  of  experiment,  that  electricity  is  de- 
veloped in  the  nervous  centres  and  circulates  in  the  nerves. 
But  up  to  the  present  time,  the  most  delicate  instruments  in 
the  hands  of  the  most  skilful  observers  have  failed  to  detect 
in  the  nerves  the  slightest  electric  current,  and  nothing 
authorizes  us  to  consider  the  nervous  force  as  identical  with 
electricity.  May  we  not  consider  them  as  at  least  analogous? 
They  may  both  be  developed  by  friction,  by  chemical  com- 
binations, by  heat,  &c. ;  both  are  rapidly  transmitted,  and 
both  cause  an  elevation  of  the  temperature,  and  the  composi- 
tion or  decomposition  of  certain  products.  But  while  it  is 
true  that  motor  impulses  are  transmitted  with  great  speed, 
comparable  to  that  of  the  electric  fluid,  the  nervous  system 
contributes  only  indirectly  to  produce  animal  heat,  and  nothing 
here  suggests  a  current  heating  a  metallic  wire.  In  fact  it 
is  only  by  hypothesis  that  we  assume  the  influence  of  nervous 
force  on  the  chemical  operations  of  life,  otherwise  than  in 
giving  activity  to  the  organs  intrusted  with  these  operations. 
But  we  must,  notwithstanding,  admit  a  certain  analogy 
between  nervous  phenomena  and  electrical  phenomena. 
Further  research  will  doubtless  throw  light  upon  this  ques- 
tion, which  is  so  eagerly  studied,  and  which  would  perhaps 
have  already  been  solved  if  we  could  compare  the  reactions 
of  inert  matter  to  the  transformations  of  organized  matter, 
and  the  phenomena  which  are  purely  physical  with  those 
in  which  life  takes  part. 

The  memory. — The  Greeks  made  Mnemosyne  the  mother 
of  the  Muses,  and  for  us,  under  a  less  poetical  form,  me- 
mory is  the  indispensable  bond  of  union  of  the  intellectual 
faculties. 

The  senses  reveal  to  us  the  external  world,  the  intellect 
apprehends  the  sensations,  and  rising  from  material  notions 
to  abstract  conceptions,  embraces  all  that  man  is  permitted 
to  learn  or  to  know;  but  it  is  the  memory  which  enables  us 
to  record,  as  in  a  book,  facts  and  results,  to  compare  and  to 
judge,  to  express  thought  by  language,  and  to  share  the 
thoughts  of  others.  Without  memory  man  would  not  recog- 


148  THE    HUMAN    BODY. 

nize  the  ties  of  blood,  of  friendship,  or  of  gratitude;  the 
past  would  have  no  existence  for  him,  his  life  would  only 
embrace  the  present  moment,  and  would  flow  on  like  the 
period  immediately  succeeding  birth.  Deprived  of  experi- 
ence, impelled  by  blind  instinct,  isolated  in  creation,  he 
could  not  exist  with  organs  which  render  necessary  every- 
thing of  which  he  would  be  deprived.  We  cannot  therefore 
imagine  the  human  race  without  memory,  and  in  order  to 
find  an  organization  without  this  faculty  we  must  descend  to 
the  lowest  grades  of  animal  life. 

Memory  is  of  a  compound  nature :  partaking  of  body  and 
of  spirit,  it  is  a  reflection,  an  image  of  ourselves,  since  it 
carries  us  back  to  every  moment  that  has  impressed  our 
lives.  An  exact  and  enthusiastic  historian  of  the  facts  which 
she  recounts  to  us,  she  seems  to  add  to  our  existence  the 
hours  already  passed,  but  as  she  approaches  epochs  she 
rudely  makes  us  sensible  of  the  flight  of  time.  It  may  be 
happiness  that  makes  us  recall  hours  of  pleasure,  or  in  mis- 
fortune we  may  remember  them  with  that  pain  of  which  the 
poet  sings.  She  shows  us  the  faces  of  all  who  have  had  a 
part  in  our  existence,  sometimes  an  isolated  portrait,  and  at 
others  a  crowded  gallery;  a  minute  object,  a  plant,  a  rock,  or 
the  grandest  scenes  in  nature;  a  word,  or  the  entire  work  of 
a  writer;  a  fact,  or  the  history  of  a  people.  She  carries  us 
back  in  an  instant  to  the  most  vivid  impressions,  or  to  the 
most  abstract  conceptions,  whether  of  the  senses  or  the  in- 
tellect. In  taking  the  form  of  sensation  or  of  thought,  she 
makes  us  traverse  time  and  space  with  a  swiftness  of  which 
nothing  material  can  give  us  an  idea;  we  might  indeed  say, 
that  time  and  space  have  no  existence  for  the  memory,  if  she 
did  not  in  surmounting  them  awaken  the  idea  of  the  one 
and  the  other.  Obeying  the  behests  of  the  will,  memory 
retraces  a  scientific  doctrine  as  a  whole  and  in  detail,  the 
nicest  distinctions  of  the  most  violent  dispute,  the  series 
of  systems  of  philosophy,  all,  in  a  word,  that  science  or 
the  most  profound  erudition  has  been  able  to  classify  in  the 
mind. 

We  find  everywhere  the  records  of  extraordinary  memories, 
great  numbers  of  which  come  down  to  us  from  antiquity. 


MEMORY.  149 

Mithridates  spoke  twenty-two  languages  or  dialects  accord- 
ing to  Aulus  Gellius,  and  forty  according  to  Pliny.  Scipio 
the  Asiatic  knew  most  of  his  legionaries  by  name;  Julius 
Caesar,  Hortensius,  Lucullus,  Adrian,  and  many  others,  prove 
that  a  powerful  memory  is  not  incompatible  with  a  superior 
mind.  Pic  de  la  Mirandole  was  a  fresh  example  in  the 
fifteenth  century,  as  were  also  Leibnitz  and  Haller  in  the 
eighteenth.  The  last-mentioned  cites  a  German,  named 
Miiller,  who  spoke  twenty  languages,  and  in  our  day  we 
have  Cardinal  Mezzofanti,  who  spoke  nearly  fifty,  exclusive 
of  dialects,  conversing  with  the  pupils  of  the  College  of 
the  Propaganda,  who  had  come  from  every  quarter  of  the 
globe. 

It  is  related  also  that  Scaliger  learned  Homer  by  heart  in 
twenty-one  days,  and  the  other  Greek  poets  in  four  months; 
and  we  are  assured  that  Magliabecchi  could  dictate  whole 
books  after  having  read  them  once;  and  if  some  of  these 
examples  of  prodigious  memory  are  not  verified,  they  are  at 
least  rendered  very  probable  by  those  which  are  incontest- 
able. 

It  was  an  extraordinary  memory  which,  enabled  the  young 
Sicilian  shepherd,  Mangiamele,  to  calculate  mentally  with 
such  rapidity,  that  the  members  of  the  Academy  of  Sciences 
could  scarcely  follow  him  even  by  the  aid  of  the  most  expe- 
ditious processes.  But  the  very  ordinary  intellect  of  this 
young  man  proves  that  in  his  case  memory  was  a  faculty  out 
of  all  proportion  to  the  others,  a  circumstance  often  observed 
especially  in  children. 

Memory  is  sometimes  awakened  by  a  sensation  which 
carries  us  back  to  the  time  and  place  where  such  or  a  similar 
sensation  was  produced.  This  memory  of  the  senses  acts 
upon  us  with  extraordinary  power,  it  is  one  of  the  most 
effective  means  which  writers  possess  of  touching  the  human 
heart.  Eneas  wept  on  beholding  a  picture  on  the  walls  of 
Carthage,  which  recalled  the  misfortunes  of  his  country. 
"En  Priamus"  Behold  Priam!  said  he,  addressing  his 
companions  in  exile.  Andromache  watered  with  her  tears 
the  grassy  mound  she  had  consecrated  to  the  memory  of 
Hector  on  the  banks  of  another  Simois;  and  the  Florentine 


150  THE   HUMAN    BODY. 

accent  of  Dante  made  the  Ghibeline  Farinata  forget  the 
tortures  of  hell. 

In  former  times  the  musicians  of  the  Swiss  troops  in  the 
service  of  France  were  forbidden,  under  severe  penalties,  to 
play  their  national  airs,  and  especially  the  "Ranz  des  Vaches," 
as  it  caused  the  soldiers  to  desert,  or  made  them  home-sick. 
Taste  and  smell  are  not  less  powerful  in  awakening  memory, 
even  after  many  years  have  passed. 

The  seat  of  memory  has  been  vainly  sought  in  the  brain. 
Gall  and  several  other  physiologists  have  placed  it  in  the 
anterior  lobes,  and  the  phrenological  school  assigns  certain 
circumscribed  portions  to  the  memory  of  words,  of  places, 
of  numbers,  and  of  persons,  &c.  But  this  localization  is  not 
justified  by  observation,  and  it  is  no  more  required  by  the 
memory  than  by  the  other  faculties.  Indeed,  the  impossi- 
bility of  attributing  to  the  brain  the  projections  which  vary 
solely  according  to  the  dimensions  of  the  frontal  sinus,  was 
one  of  the  objections  to  the  doctrine  of  Gall.  It  is  remark- 
able, also,  that  contrary  to  the  opinion  of  phrenologists,  the 
greater  or  less  prominence  of  the  eye  (that  is,  the  greater  or 
less  depth  of  the  orbit)  bears  no  relation  to  the  development 
of  the  memory.  There  is  more  foundation  for  the  observa- 
tion of  particular  aptitudes  of  memory,  specially  to  retain 
words,  facts,  numbers,  &c.  We  may  go  still  further,  if  we 
observe  the  changes  induced  by  disease,  for  in  certain  cases 
the  memory  fails  to  retain  substantives,  or  verbs,  or  other 
classes  of  words  only,  while  all  others  are  retained  without 
difficulty.  We  may  therefore  suppose  that  certain  parts  of 
the  brain  are  devoted  specially  to  each  detail  of  the  memory 
as  to  the  other  faculties,  as  to  the  sensation  of  every  nervous 
filament  which  transmits  a  tactile  impression  from  any  point 
of  the  body.  This  almost  infinitesimal  division  of  the  brain 
will  not  astonish  us  in  view  of  analogous  facts  derived  from 
observation,  or  which  reason  imposes  upon  us,  although  no 
material  demonstration  is  possible;  yet  we  must  also  admit 
that  the  brain,  as  an  organ  of  apprehension,  acts  as  a  whole, 
and  that  if  a  distinct  apparatus  exists  for  the  memory,  its 
action  is  at  once  single  and  multiform,  each  of  its  parts  re- 
ceiving with  equal  aptitude  the  impression  of  the  ideas  which 


MEMORY.  151 

are  assigned  to  it.  Is  it  not  thus  that  the  innumerable 
divisions  of  the  retina  perceive  with  equal  distinctness 
degrees  of  light?  and  is  it  not  rational  to  suppose  that  it  is 
the  same  with  the  region  of  the  brain, 'which  receives  the 
nervous  filaments  which  spring  from  every  portion  of  the 
retina? 

Very  feeble  in  the  first  stages  of  life,  the  memory  is  deve- 
loped along  with  the  cerebral  convolutions,  and  the  gray  or 
cortical  substance.  It  loses  its  facility  as  mature  age  succeeds 
to  youth,  and  retains  with  more  difficulty  the  facts  confided 
to  it  in  proportion  as  years  accumulate.  In  the  aged  it 
retains  the  impressions  acquired  during  the  first  half  of  life, 
though  in  some  fortunately  endowed  organizations  it  con- 
tinues to  increase  its  stores.  Cato  learned  Greek  in  his  old 
age;  and  Baron  Humboldt  at  fourscore  embodied  in  his 
Cosmos  the  whole  circle  of  the  sciences,  and  their  most 
recent  discoveries. 


CHAPTER    XI. 


Sense  of  sight.  —  Organ  of  vision. — Globe  of  the  eye;  sclerotic;  cornea; 
choroid ;  ciliary  ring ;  ciliary  body;  ciliary  process;  iris;  pupil;  nvea; 
pigment;  retina;  vitreous  body;  hyaloid  membrane;  crystalline;  anterior 
and  posterior  chambers;  aqueous  humour. — Muscles  of  the  eye. — Con- 
junctiva.— Eyelids,  eyelashes. — Lachrymal  apparatus.  —  Vision  ;  func- 
tions of  the  retina,  reversed  images;  functions  of  the  iris;  optic  centre, 
visual  angle,  visual  impressions,  single  or  mixed,  adaptation  of  the  eyt  to 
distances,  myopia,  presbyopia;  achromatism;  single  and  double  vision 
with  two  eyes,  stereoscope;  alternation  in  the  action  of  the  eyes;  persist- 
ence of  impressions  on  the  retina;  accidental  images;  irradiation;  acci- 
dental aureola;  Daltonism;  apparent  motion  of  objects.  —  Optic  nerve. — 
Movements  of  the  eye. — Extent  of  vision. 

Organ  of  vision. — The  visual  apparatus  consists  of  the 
globe  of  the  eye  and  its  appendages,  which  are  the  eyelids 
and  eyebrows,  the  motor  muscles  of  the  eye,  and  the  lach- 
rymal apparatus. 

The  globe  of  the  eye. — The  globe  of  the  eye  is  generally 
described  as  a  spheroid,  to  which  the  segment  of  a  smaller 
sphere  is  applied  in  front,  and  this  definition  is  exact  to  the 
senses  if  it  is  not  so  mathematically.  The  walls  of  the  globe 
of  the  eye  are  formed  principally  of  two  fibrous  membranes; 
one  white  and  opaque — the  sclerotic  (sderos,  hard)- — which 
envelops  the  two  posterior  thirds  of  the  globe;  and  the  other 
transparent,  and  resembling  a  horny  plate,  from  whence  its 
name,  cornea.  The  sclerotic  is  one  of  the  strongest  fibrous 
membranes  in  the  body;  it  is  white  on  its  external  surface, 
and  of  a  brownish-red  colour  internally;  it  is  thicker  at  the 
posterior  portion  of  the  eye,  where  it  opens  to  allow  the  pas- 
sage of  the  optic  nerve,  than  in  front,  where  it  terminates  in 
a  circular  hollow  or  slope,  into  the  border  of  which  the  cornea 
is  set  like  a  watch-glass.  The  two  membranes  are  united  by 


CHOROID. 


153 


intimate  adherence,  so  strongly  as  to  seem  but  one.  The 
cornea  is  thicker  than  the  sclerotic,  and  is  composed  of 
superposed  layers  perfectly  translucent;  it  is  convex  in  front, 
and  concave  behind,  and  appears  to  be  circular,  although  its 
transverse  diameter  is  a  little  greater  than  the  other. 

Choroid. — On  the  internal  surface  of  the  sclerotic  is  a  vas- 


Fig.  34. — Vertical  section  of  the  eye  on  the  median  line. 


A.  Cornea. 

B.  Anterior  chamber. 

C.  Pupil. 

D.  Iris. 

E.  Crystalline. 

F.  Zone  of  2 'inn,  forming  the  an- 

terior •wall  of  canal  of  Petit. 

G.  Ciliary  processes  and  circle. 
H.  Sclerotic. 


I.  Choroid. 
K.  Retina. 
L.  Vitreous  body. 
M.  Optic  nerve. 
N.  Right  inferior  imtscle. 
O.  Right  srtperior  imtscle. 
P.  Leitator  muscle  of  eyelid. 
Q.  Lachrymal  glands. 
R.  Lachrymal  canal. 


cular  membrane  called  the  choroid,  which  lines  it  closely 
from  the  bottom  of  the  eye  to  the  circumference  of  the 
cornea,  and  is  attached  to  it  by  a  very  fine  cellular  tissue. 
The  choroid  is  composed  of  two  layers,  of  which  the  external 
corresponds  to  the  sclerotic,  and  the  internal,  or  membrane 


154  THE    HUMAN    BODY. 

of  Ruysch,  corresponds  to  the  retina.  These  two  layers, 
attached  to  each  other  by  their  internal  surfaces,  are  covered 
externally  with  a  layer  of  pigment,  which  is  thicker  next  to 
the  retina  than  on  the  side  toward  the  sclerotic.  The  choroid 
is  pierced  behind  by  an  opening,  which  gives  passage  to  the 
optic  nerve;  in  front,  near  the  circumference  of  the  cornea, 
it  separates  in  order  to  form  the  ciliary  circle  and  ciliary 
processes.  The  ciliary  circle,  ring,  or  muscle,  is  a  little  band, 
vascular,  like  the  choroid,  slightly  adherent  by  its  external 
surface  to  the  sclerotic,  and  united  by  its  lesser  circumference 
to  the  cornea,  at  the  point  where  the  latter  attaches  itself  to 
the  sclerotic.  Behind  the  ciliary  circle  a  series  of  membran- 
ous rays  are  seen  joined  together,  and  forming  a  crown; 
these  are  the  ciliary  processes  (from  processus,  prolongation, 
ray),  the  whole  of  which  constitute  the  ciliary  body  or  disk. 
These  rays,  which  are  attached  to  the  choroid,  like  the  ciliary 
circle,  are  of  two  kinds;  one  into  which  the  crystalline  is 
set,  and  which  gives  attachment  to  its  capsule,  termed  the 
ciliary  processes  of  the  vitreous  body;  the  others  extend  to 
the  iris,  behind  which  they  form  a  sort  of  circular  curtain,  by 
folding  back  on  themselves,  and  adhering  to  the  larger  cir- 
cumference of  this  membrane.  Thus  fixed  by  one  border, 
the  ciliary  disk  floats  by  the  other,  like  a  fringe  behind  the 
iris,  yielding  to  the  slightest  impulse  which  may  be  com- 
municated to  it.  The  ciliary  processes  are  covered  with  a 
thick  layer  of  pigment. 

Iris. — In  the  space  between  the  ciliary  circle  and  the 
ciliary  process  the  larger  circumference  of  the  iris  is  fixed. 
This  is  a  muscular  membrane,  according  to  some  writers,  and 
vascular  according  to  others,  forming  a  vertical  partition 
behind  the  cornea.  The  iris  is  pierced  in  the  middle  by  a 
circular  opening  called  the//////.  It  represents  exactly  what 
is  called  a  diaphragm  in  optical  instruments.  Its  anterior 
surface  is  coloured  in  different  shades  according  to  the  indi- 
vidual, but  always  remarkable  for  their  delicacy  or  their 
intensity;  the  variety  of  which  has  given  to  the  membrane 
the  name  of  iris,  or  the  rainbow.  Its  posterior  face  is 
covered  with  a  layer  of  pigment,  which  is  called  the  uvea. 

It  is  well  known  that  the  pupil  dilates  in  the  dark,  and 


IRIS.       RETINA.  155 

contracts  on  the  contrary  in  a  bright  light,  only  allowing 
that  quantity  of  luminous  rays  to  enter  the  eye  which  is  neces- 
sary to  vision.  Certain  substances  also  when  taken  into  the 
system  act  similarly  on  the  iris;  such  are  opium  and  the 
Calabar  bean,  which  cause  the  pupil  to  contract;  belladonna, 
on  the  contrary,  dilates  it.  Changes  in  the  diameter  of  the 
pupillary  opening  also  result  from  certain  affections  of  the 
eye  and  brain.  Physiologists  consider  the  dilatation  and 
contraction  of  the  pupil  as  belonging  to  muscular  move- 
ments; in  fact  the  microscope  demonstrates  the  existence  of 
muscular  fibres  in  the  iris;  it  contracts  also  under  the  influ- 
ence of  electricity. 

It  has  been  remarked  that  the  posterior  surface  of  the  iris, 
the  ciliary  processes,  and  the  choroid  were  covered  with  a  layer 
of pigment.  This  name  is  also  given  to  a  dark  brown  substance, 
appearing  black  in  a  mass,  which  colours  certain  portions  of 
the  skin  in  the  white  man,  and  the  whole  tegument  of  the  negro. 
In  the  eye  this  pigment  plays  the  same  part  as  the  lamp-black 
in  the  interior  of  certain  optical  instruments,  as  the  telescope 
and  magic-lantern;  it  absorbs  the  luminous  rays,  and  prevents 
them  from  being  reflected,  which  would  confuse  the  vision. 

Retina. — The  internal  surface  of  the  choroid,  or  rather  the 
pigmentary  layer  which  covers  it,  is  lined  by  the  retina,  a 
nervous  membrane,  upon  which  the  objects  are  depicted 
that  we  see.  It  appears  to  be  formed  by  the  expansion  of 
the  optic  nerve,  which  enters  the  eye  at  its  posterior  part, 
and  forms  at  the  bottom  of  the  globe  an  enlargement,  which 
is  called  the  papilla  of  the  optic  nerve.  The  retina  develops 
itself  from  the  papilla,  around  which  it  forms  a  fold,  and  ex- 
tends over  the  cavity  of  the  eye  to  the  circumference  of  the 
ciliary  processes  of  the  vitreous  body,  where,  according  to 
Cruveilhier,  it  abruptly  terminates.  It  is  of  an  opaline  white 
colour,  semi-transparent,  and  easily  torn.  Its  centre,  which 
corresponds  to  the  antero-posterior  axis  of  the  eye,  is  to  the 
outside  of  the  papilla  of  the  optic  nerve,  where  there  is  a 
yellow  spot  (macula  luted)  and  a  depression  (fovea  centralis). 
The  yellow  spot  seems  to  be  the  point  in  the  eye  where 
vision  is  most  distinct.  Microscopists  describe  the  retina  as 
being  composed  of  five,  or  even  eight  layers,  of  which  the 


156 


THE    HUMAN    BODY. 


external  one  is  vascular,  and  in  contact  with  the  choroid;  the 
internal  one,  very  important  in  a  physiological  point  of  view, 
is  the  membrane  of  Jacob.  It  is  composed  of  cylinders,  or 
rods,  joined  together  like  the  stakes  of  a  palisade,  perpendi- 
cular to  the  plane  of  the  membrane,  and  forming  by  their 
free  extremities  a  mosaic,  each  microscopic  division  of  which 


Fig.  35- — Rods  of  Jacob  under  the  microscope. 

A.  Rods  of  Jacob.  D.  Points  of  the  retinal  mosaic  receiv- 

B.  Their  extremities  forming  surface  of  ing  different  luminous  rays. 

retina.  E.  Points  receiving  each  two  different 

C.  Retinal  mosaic  formed  by  the  rods.  rays. 

is  about  o'ooi  of  a  line  in  diameter  according  to  Robin, 
and  0*0008  of  a  line  according  to  Helmholtz;  and  repre- 
sents a  section  of  a  rod.  We  shall  see  what  part  these  ter- 
minal points  play  in  vision. 

Vitreous  body. — The  cavity  of  the  globe  of  the  eye  in  its 
three  posterior  quarters  is  occupied  by  a  substance  completely 
translucent,  the  vitreous  humor.  According  to  most  anatom- 
ists, it  is  contained  in  an  envelope  called  the  hyaloid  mem- 
brane. The  vitreous  humor  and  the  hyaloid  together  consti- 
tute what  is  called  the  vitreous  body,  which  is  perfectly  adapted 
to  the  retina  throughout  its  whole  extent,  and  in  front  takes 
the  form  of  the  posterior  surface  of  the  crystalline.  According 
to  those  anatomists  who  admit  the  existence  of  the  hyaloid, 


CRYSTALLINE.      CHAMBERS    OF    THE    EYE.      MUSCLES.        157 

it  folds  back  on  a  line  nearly  corresponding  to  the  border  of 
the  crystalline,  and  is  continuous  with  the  ciliary  zone  of 
Zinn,  or  the  ciliary  processes  of  the  vitreous  body;  this  zone 
embraces  the  border  of  the  crystalline,  around  which  it  forms 
the  cajial  of  Petit,  and  adheres  intimately  to  its  capsule. 

Crystalline. — This  is  the  name  given  to  a  double  convex 
lens,  more  curved  posteriorly  than  anteriorly,  translucent, 
and  placed  vertically  in  the  axis  of  the  eye,  so  that  the  axis 
of  the  lens  corresponds  to  the  centre  of  the  pupil.  The 
crystalline  is  formed  of  superposed  layers,  which  are  less  con- 
sistent outside  than  towards  the  centre;  it  is  contained  in  a 
capsule,  which  applies  itself  closely  without  adhering  to  it. 
The  greater  or  less  convexity  of  the  surfaces  of  the  crystalline 
modifies  the  power  of  the  eye,  determining  whether  the  vision 
is  long  or  short,  i.e.  presbyopic  or  myopic.  The  opacity  of 
the  lens,  or  of  its  capsule,  forms  the  disease  called  cataract. 
We  have  already  stated  that  its  edge  is  set  into  the  zone  of 
Zinn,  to  which  its  capsule  adheres. 

Anterior  and  posterior  chambers  of  the  eye.  —  Formerly  a 
certain  space  was  supposed  to  exist  between  the  crystalline 
and  the  iris ;  this  was  called  the  posterior  chamber  of  the  eye. 
We  now  know  that  the  posterior  surface  of  the  iris  is  in 
direct  contact  with  the  anterior  surface  of  the  crystalline,  and 
the  posterior  chamber  is  only  an  imaginary  space.  The 
interval  which  divides  the  iris  from  the  cornea  is  the  anterior 
chamber,  which  is  filled  with  a  fluid  called  the  aqueous  humor, 
translucent  like  the  vitreous  but  less  dense ;  it  is  secreted  by 
the  ciliary  processes. 

Muscles  of  the  eye.  Conjunctiva. — The  globe  of  the  eye  is 
situated  in  the  anterior  portion  of  the  orbit,  beyond  which 
it  extends,  and  its  axis,  which  is  on  the  plane  of  that  of  the 
orbit,  is  directed  inwards  towards  the  centre  of  the  base  of  the 
cranium.  The  eye  is  fixed  in  the  orbit  by  an  aponeurotic 
capsule,  the  optic  nerve,  and  by  six  muscles  which  turn  it 
in  every  direction.  A  mucous  membrane,  the  conjunctiva, 
so  named  because  it  unites  the  eye  to  the  lids,  spreads  over 
the  anterior  portion  of  the  globe,  as  is  proved  by  the  injec- 
tion of  its  vessels  in  some  ophthalmic  affections,  and  then 
folds  back  on  itself,  and  lines  the  internal  surface  of  the  eye- 


158  THE    HUMAN    BODY. 

lids.  According  to  some  anatomists,  it  is  not  the  conjunctiva, 
but  only  an  expansion  of  its  epithelium,  which  covers  the 
cornea. 

Eyelids. — An  elliptical  muscle  extends  in  front  of  the 
orbit,  which  is  formed  of  concentric  fascicles,  and  which 
presents  a  transverse  chink  closed  during  contraction,  and 
open  in  the  shape  of  an  almond  when  its  fibres  are  relaxed. 
This  is  the  orbicular  muscle  of  the  eyelids.  Its  ocular  surface 
is  covered  by  the  conjunctiva,  its  external  face  by  the  skin,  its 
opening  is  circumscribed  by  the  edge  of  the  lids,  which  are 
made  firm  by  the  tar  sal  cartilages.  The  upper  lid  is  larger  than 
the  lower,  and  is  raised  by  a  special  muscle,  the  contraction 
of  which  alternates  with  that  of  the  orbicularis,  which  is  its 
antagonist.  The  points  where  the  eyelids  are  united  by  their 
commissures  are  called  the  angles  of  the  eye.  At  the  internal 
or  greater  angle  of  the  eye,  the  conjunctiva  forms  a  fold, 
the  semi-lunar  fold,  which  is  in  fact  a  rudimentary  repre- 
sentative of  the  third  eyelid  (membrana  nictitans)  of  certain 
animals.  Inside  of  this  fold  is  the  lachrymal  caruncle,  a 
small  glandular  body  of  a  rose  colour,  which  is  covered  by 
the  conjunctiva.  The  edges  of  the  lids  are  ornamented  with 
a  fringe  of  silky  hairs  which  protect  the  eye,  and  add  greatly 
to  its  beauty.  The  greater  or  less  extent  of  the  opening  of 
the  lids  makes  the  eye  appear  larger  or  smaller;  the  confor- 
mation of  the  palpebral  muscles  and  the  tarsal  cartilages  gives 
to  the  eye  an  elongated  and  languishing  form  as  in  the  East, 
or  round  and  bold  as  among  the  Occidentals;  but  the  dimen- 
sions and  form  of  the  globe  are  the  same  in  all  countries  and 
in  all  individuals. 

The  upper  lid,  which  is  attached  to  the  arch  of  the  orbit,  is 
surmounted  by  the  eyebrow,  which  is  designed  to  protect  the 
eye  like  a  visor,  and  its  movements  play  an  important  part 
in  the  expression  of  the  face. 

Lachrymal  apparatus. — This  is  composed  of,  firstly,  the 
lachrymal  gland,  which  lies  in  a  depression  of  the  orbital  arch, 
and  of  little  glands  of  the  same  nature,  which  form  a  granular 
layer  in  the  substance  of  the  upper  lid;  secondly,  of  the  lachry- 
mal canals,  by  which  the  tears  are  poured  out  upon  the  con- , 
junctiva,  a  little  above  the  border  of  the  upper  lid;  thirdly ', 


TEARS.       VISION.  159 

the  lachrymal  ducts,  which  are  destined  to  receive  the  tears 
after  they  have  bathed  the  eye,  and  of  which  the  orifices  or 
lachrymal  points  are  seen  near  the  internal  commissure  of  the 
lids;  fourthly,  the  lachrymal  sac,  in  which  the  lachrymal 
ducts  terminate,  and  which  empties  the  tears  into  the  nasal 
canal. 

The  tears  by  running  over  the  surface  of  the  conjunctiva 
render  it  supple  and  facilitate  the  movements  of  the  globe 
and  eyelids  by  lessening  the  friction.  They  serve  the  same 
purpose  in  the  eye  as  the  synovia  does  in  the  articulations. 
The  influence  of  moral  or  physical  causes  increases  their 
secretion,  and  the  lachrymal  ducts  do  not  suffice  to  carry 
them  off  when  they  run  over  the  lids. 

Vision. — Among  the  phenomena,  all  of  which  constitute 
the  sight,  some  belong  to  the  domain  of  physics,  and  may 
be  submitted  to  investigation,  many  may  even  be  demon- 
strated by  experiment;  while  others,  on  the  contrary,  are 
patent  to  the  observation,  but  little  known  as  to  their  cause 
or  their  mechanism,  and  await  from  the  progress  of  science 
an-  explanation  which  physiology  has  as  yet  been  unable  to 
give.  Even  in  those  phenomena  which  at  first  seem  purely 
physical,  we  must  not  forget  that  the  refracting  media  of  the 
eye  are  organized,  and  cannot  be  compared  except  by 
approximation  to  inorganic  bodies,  on  the  form  and  density 
of  which  physicists  base  their  calculations.  This  is  necessarily 
the  cause  of  the  differences  in  the  theories  promulgated  in 
regard  to  vision;  for  although  the  eye  may  in  some  respects 
be  considered  as  an  optical  instrument,  we  can  never  arrive 
at  exact  deductions  by  comparing  organs  analogous  or  even 
similar  in  their  construction,  but  different  in  their  nature. 

Physicists  claim  as  belonging  to  their  proper  province  the 
visual  phenomena  produced  between  the  cornea  and  retina; 
everything  on  the  other  side  of  that  membrane  belongs  to 
physiology. 

The  retina  renders  the  eye  sensible  of  light,  and  we  may 
therefore  consider  it  as  the  essential  organ  of  vision.  The 
function  of  the  other  portions  is  to  convey  the  luminous  rays 
to  its  surface  under  conditions  necessary  to  a  nervous  im- 
pression, which  all  combine  to  insure,  but  which  is  accom- 


l6o  THE    HUMAN    BODY. 

plished  in  the  retina  alone.  Other  causes  besides  the  contact 
of  luminous  waves  may  excite  the  retina;  thus  the  pressure  of 
the  finger  on  the  eye  for  example,  and  the  disturbance  re- 
sulting from  a  fall  or  a  blow  on  the  head,  the  action  of  elec- 
tricity, and  certain  affections  of  the  eye  and  brain,  give  rise, 
in  the  absence  of  natural  or  artificial  light,  to  luminous 
images  varying  in  form  and  intensity.  Light  produced 
under  these  conditions  is  called  "retinal  light." 

Like  the  optic  and  the  other  special  nerves  of  the  organs 
of  sense,  the  retina  has  a  special  sensibility;  it  receives  the 
impression  from  the  light  and  transmits  it  to  the  brain,  but  it 
is  not  itself  sensitive  to  touch.  No  mechanical  irritation 
causes  it  the  slightest  pain.  In  a  normal  condition,  the  action 
of  a  too  brilliant  light,  and  in  certain  affections  of  the  eye 
and  brain,  the  least  ray  will  cause  a  painful  sensation,  but 
this  pain  must  be  referred  either  to  the  encephalon  or  to 
the  nerves  of  the  iris  or  of  the  ciliary  circle,  independent  of 
the  retina  and  the  optic  nerve. 

Punctum  cctcum  or  blind  point.— Mariotte  was  the  first  to 
recognize  that  all  parts  of  the  retina  were  not  equally  sensi- 
tive. According  to  most  authors,  a  limited  portion  of  this 
membrane,  corresponding  to  the  papilla  of  the  optic  nerve, 
is  totally  insensible  to  light.  M.  Longet  admits  that  there 
it  has,  at  any  rate,  a  very  obtuse  sensibility.  This  "blind 
point"  is  the  only  one  on  the  internal  surface  of  the  eye 
which  is  not  covered  with  pigment. 

If  we  trace  two  figures  on  a  horizontal  line  on  a  piece  of 
paper  placed  vertically  (fig.  36,  p.  161),  and  then  shut  the 
right  eye,  and  fix  the  left  on  the  right  figure,  at  certain  dis- 
tances we  can  see  both  of  them  more  or  less  distinctly;  but 
varying  the  distance  of  the  paper  from  the  eye,  there  is  a  point 
when  we  only  see  the  figure  upon  which  the  eye  is  fixed ;  the 
other  disappearing  entirely,  but  it  reappears  when  we  change 
the  position  of  the  paper,  or  cease  to  look  fixedly  at  one  figure. 
The  greater  the  distance  between  the  two  figures,  the  greater 
must  be  the  distance  of  the  paper  from  the  eye,  in  order  to 
render  one  of  them  invisible.  The  image  of  the  invisible 
one  is  then  projected  on  the  blind  point,  and  it  reappears, 
when  by  the  displacement  of  the  paper  the  angle  which  its 


ENTOPTICS.   REVERSED  IMAGES. 


161 


rays  form  with  those  from  the  other  becomes  more  or  less 
open. 

Ent optics. — The  eye  perceives  not  only  external  objects,  but 
certain  details  of  its  internal  organization. 
This  portion  of  the  visual  phenomena  is 
called  interior  vision,  or  entoptics.  A 
bruise  of  the  cornea  through  the  lids,  or  a 
scar  or  foreign  body  on  its  surface,  the 
vascular  ramifications  of  the  retina,  and 
other  causes  of  that  nature,  sometimes 
throw  images  on  the  retina  of  different 
forms,  such  as  striae,  spots,  globules,  dark 
or  luminous  circles  which  appear  to  move 
in  the  eye.  Certain  of  these  images  are 
called  ilies,  or  motes  (musccR  voliiantes\ 
because  they  traverse  the  field  of  vision 
from  one  side  to  the  other.  Their  ap- 
pearance results  from  nothing  abnormal, 
and  they  cannot  be  confounded,  when 
there  is  no  other  disturbance  of  the  visual 
functions,  with  the  analogous  signs  which 
accompany  and  denote  some  diseases  of 
the  eye  and  brain.  A.  lateral  movement 
of  the  eye  is  sufficient  to  displace  them  or 
cause  them  to  disappear. 

Reversed  images.  —  The  eye  may  be 
compared  to  an  optical  instrument  known 
as  the  camera  obscura.  It  is  well  known 
that  the  image  of  objects  appears  re- 
versed on  the  screen  of  the  camera;  in 
the  same  manner  the  luminous  rays  which 
spring  from  every  point  of  an  object  at 
which  we  look,  traverse  the  cornea,  the 
aqueous  humor,  the  crystalline,  and  the  Fig.  36. 

vitreous  body,  in  order  to  reach  the  re- 
tina ;  and  are  refracted  in  this  transit,  so  that  the  image  which 
they  form  appears  reversed  at  the  bottom  of  the  eye.     In 
examining  the  eye  of  an  ox,  of  which  the  sclerotic  has  been 
previously  made  thin — or  the  eyes  of  albinoes,  such  as  white 

11 


1 62  THE    HUMAN    BODY. 

rabbits,  for  example,  which  are  destitute  of  pigment,  and  in 
which  the  sclerotic  and  choroid  are  transparent,  we  may  see, 
as  Magendie  pointed  out,  the  flame  of  a  candle  reversed  upon 
the  retina. 

How  then  are  we  able  to  see  objects  in  their  real  position? 
BufTon  and  others  have  asserted  that  reason  enables  us  to 
restore  the  image  depicted  on  the  retina  to  its  real  position, 
that  touch  enables  us  to  rectify  the  visual  sensation.  But 
Cheselden,  having  by  an  operation  enabled  a  patient  born 
blind  to  see,  does  not  state  that  the  young  man  first  saw 
objects  otherwise  than  in  their  real  position;  and  the  careful 
observations  made  by  this  skilful  surgeon  do  not  permit  us 


Fig.  37. — Course  of  the  luminous  rays  in  the  eye. 

H,  M,  P.  Luminous  rays  emanating  from  an  object, 
h,  m,  p.  Lviminous  rays  refracted,  forming  the  inverted 
image  on  the  retina. 

to  suppose  that  a  circumstance  of  such  importance  could 
escape  his  notice.  According  to  M.  Lame,  we  know  that 
objects  are  upright  although  we  see  them  inverted,  from  the 
consciousness  of  the  movements  which  we  give  to  the  optical 
axes  of  our  eyes  in  looking  successively  at  the  different 
points  of  objects  from  top  to  bottom. 

Miiller  avers  that  we  see  the  objects  inverted,  but  that  all 
presenting  themselves  to  us  under  the  same  relative  condi- 
tions of  position,  nothing  can  appear  inverted  because  we 
see  everything  in  the  same  position,  and  that  our  notions  of 
uprightness  or  inversion  only  exist  by  opposition. 


THEORY  OF  UPRIGHT  VISION.     FUNCTIONS  OF  IRIS.         .163 

M.  Longet  explains  upright  vision  by  supposing  that  every 
external  luminous  point  is  felt  in  the  eye  according  to  the 
direction  it  takes  relative  to  us.  We  must,  says  this  eminent 
physiologist,  consider  the  concave  spherical  surface  of  the 
retina  as  formed  of  a  mosaic,  each  elementary  part  of  which 
is  a  sort  of  eye  designed  to  perceive  the  different  luminous 
impressions  in  a  determinate  direction.  Every  pencil  of 
light  emanating  from  a  luminous  point,  and  forming  a  cone 
of  which  the  apex  and  the  normal  axis  correspond  to  one  of 
these  portions,  will  be  perceived  in  the  direction  of  a  line 
joining  the  centre  of  the  spherical  surface  to  the  object 
looked  at.  If  we  reason  in  this  way  for  every  one  of  the 
points  which  constitute  the  whole  of  a  visible  object,  the 
perception  of  each  of  these  points  will  be  in  the  real  direc- 
tion, and  that  of  the  whole  will  also  be  felt  under  the  same 
conditions,  in  regard  to  the  observer.  The  image  therefore 
is  not  seen  as  a  complete  whole ;  each  luminous  point  assist- 
ing in  its  formation  milking  a  separate  impression  on  the 
brain,  each  one  is  felt  according  to  the  primitive  direction  of 
the  ray  of  light,  and  the  whole  is  seen  in  its  real  position. 

Functions  of  the  iris. — In  order  that  vision  may  be  distinct, 
it  is  necessary  that  the  rays  should  enter  the  eye  in  the 
direction  of  what  is  termed  the  visual  axis,  and  the  various 
movements  of  the  organ  tend  unceasingly  to  place  it  in  a 
position  to  fulfil  this  condition,  and  it  is  necessary,  also,  that 
the  light  should  be  neither  too  strong  nor  too  weak,  and  that 
the  rays  shall  traverse  the  central  portion  only  of  the 
crystalline,  and  not  its  borders.  In  order  to  obtain  an 
analogous  result  in  some  of  their  instruments,  opticians 
divide  them  by  means  of  a  partition  pierced  by  a  hole  in 
the  centre,  which  is  termed  a  diaphragm.  We  find  a  similar 
arrangement  in  the  eye,  "  an  intelligent  diaphragm,"  to  use 
the  expression  of  M.  Longet,  that  is  the  iris,  which  dilates 
or  contracts  the  pupil  in  such  a  manner  as  to  measure  the 
quantity  of  light  necessary  to  vision,  and  which  only  allows 
those  rays  to  pass  which  are  directed  toward  the  central 
portion  of  the  crystalline  lens.  In  the  dark,  or  if  we  look  at 
an  object  but  slightly  illuminated,  the  pupil  dilates  in  order 
to  admit  the  greatest  possible  number  of  rays  which  are 


164  THE    HUMAN    BODY. 

refracted  by  the  cornea;  it  is  the  same  if  we  look  at  a 
distant  object,  the  rays  from  which  are  less  divergent;  if  this 
object  becomes  more  luminous,  or  if  we  approach  it,  the 
pupil  contracts  in  proportion. 

Optic  centre,  visual  angle,  appreciation  of  the  size  of  objects. 

—The  rays  emanating  from  two  points  of  an  object,  p  H  (fig. 

38),  converge  toward  the  optic  centre  o,  at  a  point  in  the  eye 

a  little  behind  the  crystalline,  and  thus  form  an  angle  P  o  H, 

which  is  called  the  visual  angle.    From  the  optic  centre  these 


rays  diverge  to  the  retina,  and  form  an  angle,  /  o  //,  equal  to 
the  first,  the  base  of  which,  corresponding  to  the  retina, 
measures  the  size  of  the  image  which  they  form  upon  it.  The 
visual  angle  therefore  gives  us  an  idea  of  the  size  of  objects, 
and  enables  us  to  compare  them,  but  in  order  that  our  ideas 
may  be  exact,  they  must  be  confirmed  by  our  notions  of  dis- 
tance. In  fact,  several  objects  of  unequal  size,  P  H,  P'H', 
P"H",  may  be  placed  at  such  distances,  ABC  (fig.  38),  as  to 
subtend  the  same  visual  angle;  we  must  therefore  estimate 
their  relative  distance,  in  order  to  judge  correctly  of  their 
size.  We  can  also  obtain  a  knowledge  of  their  size,  if  we  know 
that  of  any  portion  of  the  object  which  we  see,  or  the  size 
of  another  object  placed  at  an  equal  distance.  Thus,  when 
we  look  at  a  ship  at  sea,  we  can  judge  of  its  size  by  that  of 
the  men  whom  we  see  upon  it;  the  height  of  a  balustrade 
enables  us  to  calculate  approximately  that  of  the  building  of 
which  it  forms  a  part.  When  the  means  of  comparison  fail 


ESTIMATION    OF    SIZE.       VISUAL    IMPRESSIONS.  1 05 

us,  it  is  very  difficult  to  avoid  errors,  the  very  causes  of 
which  escape  us.  Thus,  the  sun  and  the  moon  when  they 
are  near  the  horizon,  seem  to  present  a  much  greater  diameter 
than  when  high  in  the  heavens.  The  atmosphere  causes 
objects  to  appear  near  or  distant,  according  as  it  is  pure,  or 
charged  with  mist.  These  illusions  are  frequent,  especially 
among  mountains,  and  the  inexperienced  traveller  should  not 
count  too  much  upon  the  exactness  of  his  impressions. 

Bravais  points  out  a  very  common  error  in  drawing  a 
rough  hill-side  in  relief,  or  a  mountainous  horizon.  In  veri- 
fying a  sketch  mathematically,  the  horizontal  distances  of 
the  different  points  in  the  landscape  are  found  to  be  suffi- 
ciently exact,  while  the  height  of  the  summits,  or  of  inequalities 
of  surface,  is  in  double  proportion.  But  we  must  add,  that  the 
design  adjusted  mathematically  seems  incorrect  in  an  opposite 
sense,  and  does  not  give  the  impression  of  the  natural  relief. 

If  a  rainbow  is  formed  over  a  cascade  when  the  sun  is 
near  the  horizon,  and  the  circle  of  this  bow  is  nearly  com- 
plete, we  seem  to  see  not  a  circle,  but  an  ellipse,  of  which 
the  principal  axis  is  vertical;  the  same  illusion  is  produced 
when  we  look  at  a  halo. 

Visual  impressions,  separate  or  mixed. — If  we  look  at  a 
print  placed  at  a  certain  distance,  the  details  of  the  engraver's 
work  disappears,  the  dots  and  the  shading  are  confounded 
with  the  white  lines  which  separate  them,  and  the  eye  per- 
ceives only  a  grayish  tint  more  or  less  distinct;  so  also,  if  a 
red  and  blue  powder  be  mingled  together,  the  mixture  gives 
us  the  impression  of  a  violet  colour,  although  every  grain  of 
each  powder  preserves  its  own  proper  colour.  This  is  ex- 
plained as  follows.  We  have  already  stated  that  the  internal 
surface  of  the  retina  presents  a  mosaic  of  extremely  small 
terminal  divisions,  each  one  of  which  acts  separately,  and 
transmits  to  the  brain  one  single  impression  at  a  time.  If 
the  image  of  a  trace  of  the  burin  or  of  a  grain  of  powder 
covers  one  of  these  divisions,  the  impression  is  single  (see 
%•  35?  P-  J56);  but  if  two  lines,  one  white  and  the  other 
black,  or  two  grains,  one  red  and  the  other  blue,  are  so 
small  and  so  near  together,  that  their  images  are  in  juxtaposi- 
tion on  the  same  division  of  the  retina,  the  impression  is 


1 66  THE   HUMAN    BODY. 

mixed,  and  the  brain  perceives  the  sensation  of  gray  or  of 
violet.  Or,  in  other  words,  in  order  that  two  minute  luminous 
objects  may  be  distinctly  seen,  the  angle  subtended  upon  the 
retina  by  their  images  must  not  be  greater  than  the  diameter 
of  one  of  the  retinal  divisions.  The  distance  of  the  two 
objects  from  the  eye  being  determined,  the  measure  of  the 
angle  subtended  by  them  enables  us  to  estimate  the  size  of 
these  divisions. 

Accommodation  of  the  eye  to  distances. — When  we  make  use 
of  the  camera  obscura,  in  order  that  the  image  may  be  dis- 
tinct the  screen  must  be  placed  in  the  focus  of  the  instru- 
ment, that  is  at  the  point  where  all  the  rays  refracted  by  the 
objective  converge.  If  the  objects  recede  or  approach,  the 
screen  must  be  placed  at  a  proportionate  distance  from  the 
object-glass,  so  that  its  surface  may  correspond  to  the  apices 
of  the  refracted  luminous  cones.  And  yet  we  see  with  equal 
distinctness  the  images  of  objects  at  very  unequal  distances, 
without  any  variation  in  the  form  of  the  eye,  or  the  relative 
conditions  of  its  media,  or  at  least  without  our  consciousness 
of  anything  but  a  scarcely  perceptible  effort.  This  power  of 
accommodation  of  the  eye  has  long  been  the  subject  of  inves- 
tigation, and  the  question  is  not  yet  settled.  The  most 
generally  received  explanation  is,  that  in  order  to  see  objects 
at  different  distances,  and  especially  very  near  to  the  eye,  it 
modifies  its  form,  or  that  of  its  media,  and  adapts  itself  to  the 
distance  in  such  a  manner,  that  the  retina  is  always  in  the 
focus.  According  to  some  authors,  the  length  of  the  axis  of 
the  eye  varies,  the  retina  approaching  or  receding  from  the 
crystalline.  Others  maintain  that  it  is  the  crystalline  which 
changes  its  place,  or  that  the  curves  of  the  refracting  media 
modify  themselves  in  such  a  manner,  as  always  to  make  the 
apices  of  the  luminous  cones  coincide  with  the  immovable 
retinal  surface.  This  theory  of  adaptation  or  accommodation 
is  denied  by  some  eminent  savants,  though  a  few  of  them 
approach  it  in  attributing  this  phenomenon  to  the  contrac- 
tion and  dilatation  of  the  pupil;  while  others  have  endeavoured 
to  demonstrate  that  the  distance  of  objects  from  the  eye  may 
vary  to  a  great  extent,  without  the  image  undergoing  any 
appreciable  modification. 


ACCOMMODATION.  167 

Helmholtz  maintains  that  the  anterior  surface  of  the  crys- 
talline increases  in  convexity  in  looking  at  objects  near  at 
hand,  and  flattens  when  looking  at  a  distance;  the  pupil 
contributes  also  to  the  accommodation  by  contracting  in 
looking  at  objects  near  at  hand,  and  dilating  to  see  at  a 
great  distance.  Nothing  positive  is  known  regarding  the 
manner  in  which  this  change  of  form  in  the  crystalline  is 
effected.  M.  Helmholtz  inclines  to  the  opinion  that  the 
diameter  of  the  lens  is  increased  or  diminished,  and  conse- 
quently it  becomes  more  convex,  or  more  flattened,  accord- 
ing as  the  zone  of  Zinn,  which  is  inserted  into  the  crystalline 
capsule,  is  distended  or  relaxed  by  the  action  of  the  ciliary 
muscle. 

Some  simple  experiments  prove  that  the  eye  cannot  see 
distinctly,  without  an  effort  of  adaptation,  two  objects  placed 
at  unequal  distances,  and  that  the  image  distinctly  perceived 
by  the  retina  when  placed  in  the  focus,  is  so  no  longer  when 
the  focal  distance  is  changed. 

i.  If  we  look  with  one  eye  at  the  heads  of  two  black  pins, 
placed  in  a  line  at  the  same  level,  but  at  different  distances,  we 
shall  see  one  of  them  distinctly  and  the  other  vaguely.  If  we 


Fig.  39. — Accommodation  of  the  eye  to  different  distances. 

look  at  the  nearest  one  the  image  is  perfectly  clear,  while  the 
one  farthest  away  is  enveloped  in  mist;  but  if  we  look  at  the 
latter  we  see  it  easily  without  change  of  position,  but  when  its 
image  is  well  denned  that  of  the  other  pin  becomes  confused. 

2.  In  looking  at  a  pin  through  a  small  hole  pierced  in  a 
card,  we  can  see  either  the  pin  or  the  edge  of  the  hole  dis- 
tinctly; but  when  the  image  of  one  is  distinct  the  other  is 
confused. 

3.  By  making  two  pin-holes  through  a  card,  at  a  distanc  \ 


1 68  THE    HUMAN    BODY. 

less  than  the  diameter  of  the  pupil,  that  is,  not  more  than  one- 
twelfth  of  an  inch  from  each  other,  then  look  through  these 
two  apertures  at  a  small  object  on  a  bright  ground,  at  a  black 
point,  for  example,  on  a  sheet  of  white  paper.  At  a  certain 
distance  the  point  is  single,  but  if  the  head  be  moved  back- 
ward or  forward  it  will  appear  double. 

In  the  first  two  experiments  the  eye  is  compelled  to  adapt 
itself  to  the  distance,  in  order  to  see  distinctly  and  succes- 
sively two  objects  at  unequal  distances,  and  of  which  the 
images  are  not  distinct,  except  when  the  apex  of  the  cones 
formed  by  the  refracted  rays  of  light  exactly  corresponds  to 
the  surface  of  the  retina,  that  is,  when  the  retina  is  exactly  in 
the  focus.  And  also,  the  experiment  of  looking  through  a 
pierced  card  at  an  object,  and  seeing  it  distinctly,  that  is, 
looking  at  it  through  an  immovable  artificial  pupil,  seems  to 
prove  that  the  movements  of  the  pupil  are  not  necessary  to 
accommodation. 

The  third  experiment  proves,  that  in  order  to  see  a  single 
image  the  retina  must  be  in  focus.  In  this  case,  in  fact,  the 
rays  coming  from  the  external  object  converge  and  meet  on 
the  same  retinal  divisions,  hence  there  is  but  a  single  sensa- 
tion; if  the  eye  approaches  or  recedes,  they  reach  the  retina 
either  before  their  convergence  is  effected,  or  not  until, 
having  converged,  they  cross  each  other,  and  diverge  beyond 
the  focus,  in  either  case  in  such  a  manner  as  to  fall  upon 
different  divisions  of  the  retina,  and  in  consequence  produce 
a  double  sensation. 

The  accommodation  of  the  eye  therefore  seems  to  be  in- 
contestable, in  spite  of  the  want  of  accord  in  the  opinions  of 
savants  upon  its  mechanism.  A  very  little  attention  enables 
us  to  recognize  the  effort  which  accompanies  it,  especially  if 
the  adaptation  is  prolonged  without  variation  at  a  short  dis- 
tance, as  in  looking  through  a  microscope.  Then,  in  fact, 
the  eye  loses  sometimes  for  several  hours  the  faculty  of 
adapting  itself  to  great  distances;  it  becomes  myopic  for  a 
certain  time.  Persons  who  are  in  the  habit  of  using  a  glass 
for  one  eye,  as  watchmakers  and  engravers  for  example,  are 
generally  myopic  in  that  eye;  and  this  effect  is  very  marked 
in  infants,  who  acquire  the  habit  of  looking  at  objects  near 


MYOPIA.       PRESBYOPIA.  169 

at  hand.  Short-sightedness  is  thus  much  more  common  in 
towns  than  in  the  country.  Sailors,  mountaineers,  and  in- 
habitants of  deserts  are  generally  very  long-sighted;  the 
habit  of  looking  at  great  distances  doubtless  develops  this 
faculty. 

Myopia,  presbyopia. — The  range  of  sight  at  which  we  read 
or  write  is,  in  a  normal  condition,  about  12  to  14  inches; 
this  point  in  myopia  is  much  nearer,  and  in  presbyopia 
much  farther  off;  but  for  the  latter,  distinct  vision  does  not 
go  beyond  28  to  32  inches,  that  is,  about  double  the  dis- 
tance considered  normal;  in  myopia,  on  the  contrary,  this 
distance  may  diminish  to  within  an  inch.  This  condition 
of  the  sight  is  the  result  of  modifications  of  the  media  of 
the  eye.  In  myopia  the  cornea  or  the  crystalline  is  more, 
and  in  presbyopia  less,  convex  than  in  the  normal  condition. 
In  myopia,  therefore,  the  focus  is  in  front  of  the  retina 
for  objects  which,  not  being  very  near  the  eye,  send  to  it 
rays  which  diverge  but  slightly;  in  presbyopia,  on  the  con- 
trary, the  slight  refraction  caused  by  the  flattening  of  the 
cornea,  or  the  crystalline,  tends  to  place  the  focus  behind 
the  retina,  the  point  of  convergence  of  rays  coming  from 
objects  near  at  hand.  The  faculty  of  accommodation  is 
rather  limited  in  myopia,  as  well  as  in  presbyopia,  and  is 
necessarily  almost  entirely  wanting  in  the  very  near-sighted. 

To  remedy  these  modifications  of  the  eye,  the  short- 
sighted person  requires  double  concave  glasses,  which  increase 
the  divergence  of  the  rays  in  proportion  to  the  refraction  by 
the  media  of  the  eye;  the  long-sighted  person  requires 
double  convex  glasses,  which  produce  the  opposite  effect. 

It  is  not  uncommon  to  find  persons  who  can  only  read 
and  write  at  a  very  short  distance,  but  who  can  notwith- 
standing see  objects  at  a  distance  perfectly  well.  In  this 
case  only  one  eye  is  myopic,  the  other  is  normal.  A  slight 
inequality  in  the  eyes  is  very  common,  and  often  unper- 
ceived.  This  is  undoubtedly  the  reason  that  many  persons 
use  but  one  eye  even  when  looking  with  both,  without  being 
conscious  of  it,  and  this  inequality,  which  is  either  the  cause 
or  effect  of  this  exclusive  action,  can  only  be  augmented 
by  it. 


1 70  THE    HUMAN    BODY. 

Short-sightedness,  even  when  slight,  is  an  infirmity  from 
which  its  subjects  suffer  all  their  lives,  and  it  may  be  aggra- 
vated by  the  use  of  too  strong  glasses,  and,  as  we  have 
already  stated,  by  the  use  of  the  microscope.  Long-sighted- 
ness, on  the  contrary,  does  not  make  itself  felt  much  before 
the  age  of  forty,  and  then  only  in  persons  whose  sight  is 
good.  It  is,  as  the  name  presbyopia  indicates,  a  mark  of 
age,  and  a  little  philosophy  enables  us  to  resign  ourselves  to 
it,  and  wear  the  glasses  which  were  useless  in  youth. 

Achromatism. — In  ordinary  vision  objects  appear  to  us  in 
their  natural  colours  distinctly  defined,  and  not  surrounded 
with  the  iris-like  fringe  which  results  from  the  decomposition 


Fig.  40. 

<7,  a.  Globes  of  the  eye. 
bb,  b'  b' .  Objects  placed  in  front  of  or  beyond  the  point  of  convergence  of 

tJie  two  axes, 
c.  Point  of  convergence. 

of  light.  It  would  seem  therefore  that  the  eye  is  achromatic. 
But  the  experiments  of  Arago,  Frauenhofer,  and  other  scien- 
tific men,  prove  that  it  does  not  absolutely  possess  this  pro- 
perty, though  it  is  only  when  placed  under  abnormal  condi- 
tions that  we  discover  this.  If,  for  example,  we  look  at  an 
object,  and  adapt  the  eye  to  an  imaginary  point,  either  in 
front  of  or  beyond  it,  the  image  both  becomes  indistinct, 
and  its  edges  become  rainbow-like.  If  a  body  is  placed 
near  the  cornea,  in  such  a  way  as  to  cover  a  portion  of  the 
pupil,  the  same  effect  is  produced. 

Single  or  double  vision  with  two  eyes. — Although  a  separate 
image  is  produced  in  each  eye  when  we  look  at  an  object, 
the  object  appears  single  under  normal  conditions  of  the 


SINGLE  VISION  WITH  TWO  EYES.      STEREOSCOPE.  171 

sight,  that  is  to  say,  when  it  is  placed  at  the  point  at  which 
-the  optical  axes  converge;  but  if  the  direction  of  one  of 
these  axes  is  changed,  from  pressing  lightly  with  the  point  of 
the  finger  on  the  external  angle  of  one  of  the  eyes,  for  in- 
stance, the  object  appears  double,  and  the  images  are  sepa- 
rated more  and  more  as  the  pressure  is  increased,  and  as  it 
changes  the  direction  of  the  axis  more  and  more.  On  the 
other  hand,  two  objects,  one  placed  in  front,  and  the  other 
beyond  the  point  of  convergence  of  the  two  axes,  but  in 
the  same  direction,  give  but  one  impression,  and  we  see  but 
one. 

Double  or  single  vision  with  two  eyes  is  explained  by  the 
correspondence  of  the  terminal  divisions  of  the  retina  in  each 
eye.  These  are  called  the  identical  points.  When  the  rays 
of  light  strike  corresponding  divisions  in  each  eye,  the  sensa- 
tion is  single,  but  when  they  strike  portions  which  do  not 
correspond,  it  is  double.  This  correspondence  of  the  parts 
of  the  retina  is  shown  by  pressing  lightly  with  the  fingers  on 
the  closed  eyes.  If  the  internal  or  external  angle  of  the  eyes 
be  pressed  simultaneously,  luminous  images  will  be  formed  at 
the  points  directly  opposite  those  which  are  pressed,  and  if 
the  pressure  be  applied  to  the  internal  angle  of  one  eye  and 
the  external  angle  of  the  other,  or  if  we  press  the  upper  por- 
tion of  one  and  the  lower  portion  of  the  other,  we  see  but  a 
single  image.  From  this  we  conclude  that  in  the  first  ex- 
periment the  two  points  pressed  upon  do  not  coincide  because 
we  see  two  distinct  images,  and  that  in  the  second  they  do 
correspond  because  we  see  but  one.  According  to  Miiller, 
if  we  consider  the  retina  as  a  sphere,  the  pole  of  which  is  the 
middle  of  the  membrane  or  at  some  point  in  the  same  direc- 
tion and  at  the  same  distance  from  the  middle,  the  corres- 
ponding or  identical  points,  on  a  section  of  this  sphere, 
occupy  the  same  meridian  and  the  same  parallel.  Thus,  in 
seeing  with  two  eyes,  the  two  images  cause  but  a  single 
sensation  when  they  are  formed  on  the  corresponding  por- 
tions of  the  retina,  and  consequently  we  receive  a  double 
sensation  when  they  are  placed  on  divisions  which  are  not 
identical. 

Stereoscope. — From  what  has  been  already  stated  it  would 


172  THE    HUMAN    BODY. 

seem  that  in  order  to  give  but  a  single  impression,  the  images 
perceived  by  both  eyes  should  be  exactly  alike.  But  experi- 
ment demonstrates  that  two  images  differing  in  some  respects, 
do  notwithstanding  give  but  a  single  sensation  to  the  brain. 
When  we  look  at  a  solid  like  the  pedestal  of  a  column  or  a 
monument,  a  moment's  attention  shows  us  that  the  outlines 
corresponding  to  the  right  of  the  spectator  give  a  larger  image 
to  the  right  eye  than  to  the  left,  and  that  each  image  differs 
from  the  other;  the  combination  of  the  two  sensations  gives 
us  the  idea  of  relief. 

If  now  we  obtain  by  photography,  or  if  we  trace  by  a  single 
white  line  on  a  black  ground,  the  projection  of  this  monument 
or  pedestal,  in  conditions  identical  with  those  under  which 
our  eyes  receive  a  double  impression,  the  two  images  placed 
in  the  direction  of  the  optical  axes,  as  the  surfaces  would  be 
which  they  represent,  will  give  us  the  impression  of  the  solid 
in  question  by  a  single  image.  We  owe  to  Mr.  Wheatstone 
the  demonstration  of  this  phenomenon,  and  the  invention  of 
an  instrument  which  renders  the  proof  very  easy  and  simple. 
This  is  the  stereoscope,  the  application  of  which  is  so  widely 
known. 

When  the  eyes  are  first  applied  to  the  instrument,  in  pro- 
portion as  the  optic  axes  converge,  the  two  images  are  seen 
one  over  the  other,  and  when  at  last  we  perceive  but  one, 
instead  of  a  plane  surface  we  have  a  relief  under  our  eyes, 
which,  in  certain  cases,  produces  a  complete  illusion.  But 
as  M.  Longet  observes,  the  unity  of  the  image  does  not 
prove  that  there  is  but  a  single  sensation,  and  the  two  dif- 
ferent images  do  not  give  birth  to  a  simple  sensation,  but  are 
the  source  of  one  complex  though  indefinable  one,  that  of 
solidity.  How  this  blending  of  two  different  impressions  is 
effected,  is  one  of  the  mysteries  of  our  organization ;  but  the 
sensation  of  relief  evidently  arises  from  a  combination  of 
conditions  different  from  those  which  determine  single  vision 
by  means  of  two  eyes. 

When  vision  embraces  a  certain  extent  of  space,  as  a  land- 
scape or  a  gallery  of  pictures  for  instance,  the  objects  appear 
single  to  us,  although  for  the  most  part  they  are  out  of  the 
direction  of  the  optical  axes,  but  on  observing  closely  we  find 


ALTERNATION    IN    ACTION    OF    THE    EYES.  173 

that  we  never  fix  the  eyes  except  on  a  very  limited  portion 
of  the  space  spread  out  before  us;  the  objects  thus  normally 
seen  occupy  our  whole  attention,  and  turn  it  away  from  the 
other  images  of  which  the  vagueness  or  duplication  passes 
unperceived.  When  we  endeavour  to  determine  these  facts 
we  find  that  the  boundary  lines  of  the  objects  and  the  borders 
of  the  pictures  appear  double,  but  dim  and  confused,  when 
outside  of  the  point  of  convergence  of  the  ocular  axes. 

Alternation  in  the  action  of  the  eyes. — When  we  look  at  two 
circles  in  the  stereoscope,  alike  in  size  but  of  different  colours, 
or  if  they  are  traced  on  white  paper,  and  contain  two  different 
letters,  we  distinguish  alternately  one  image  and  then  the 
other,  and  when  after  a  longer  or  shorter  time  we  succeed  in 
seeing  them  superposed,  very  soon  they  again  alternate.  The 
two  eyes  do  not  act  simultaneously  in  experiments  of  this 
nature,  and  it  is  sometimes  the  impression  produced  on  the 
right  eye,  and  sometimes  that  of  the  left,  alone  which  reaches 
the  brain.  This  periodicity  is  especially  regular  in  persons 
whose  sight  has  the  same  range  in  both  eyes.  And  we 
remark  also  that  the  distinct  image  is  covered  with  spots  of 
the  same  colour  as  that  which  is  invisible. 

This  last  phenomenon  seems  to  indicate  that  the  retina  is 
not  equally  sensitive  throughout  its  whole  extent.  The  alter- 
native preponderance  of  one  eye  over  the  other  in  vision  is 
due  to  causes  not  thoroughly  known,  though  it  may  be 
attributed,  partially  at  least,  to  the  fact  that  the  eyes  are 
•  .  unequal  in  extent  of  vision,  or  rather  in  skill  in  seeing.  We 
ostly  all  of  us  use  one  eye  more  than  the  other  in  ordinary 
vision,  and  especially  when  we  look  attentively  at  an  object. 
It  is  with  the  eyes  nearly  the  same  as  with  the  hands  in  this 
respect,  one  is  exercised  more  than  the  other,  and  it  is 
generally  the  right  eye.  We  have  seen  that  the  difference 
between  the  two  eyes  may  amount  to  myopia  in  one  while 
the  other  is  perfectly  normal.  This  inequality,  even  if  slight, 
must  tend  to  a  difference  in  the  power  of  accommodation 
and  to  discord  in  action  which  constantly  inclines  to  cease 
and  then  to  again  reproduce  itself. 

As  for  the  inequality  in  sensibility  of  the  different  portions 
of  the  retina  outside  of  the  blind  point  (punctum  ccecum)  the 


174  THE    HUMAN    BODY. 

displacement  of  the  spots  proves  that  it  is  not  permanent. 
We  know  also  that  this  partial  insensibility  may  be  induced 
by  a  brilliant  light,  and  particularly  by  the  rays  of  the  sun. 
It  is  an  experiment  we  all  make  involuntarily,  and  which  will 
be  discussed  in  another  place. 

Persistence  of  retinal  impressions. — The  impressions  made 
by  the  luminous  rays  remain  for  a  certain  time,  and  are  then 
gradually  effaced;  it  is  plain  then,  that  if  the  action  is  repro- 
duced at  shorter  intervals  than  the  duration  of  the  impres- 
sions, the  brain  perceives,  not  a  series  of  sensations,  but  a 
continuous  one.  Thus  in  the  rapid  rotary  movement  of  a 
burning  coal,  the  eye  perceives  only  a  luminous  circle,  and 
when  a  wheel  revolves  rapidly,  the  spokes  seem  to  approach 
each  other  and  form  a  continuous  surface.  The  impression 
of  colour  persists  as  well  as  of  form  ;  and  if  we  cause  a  circle 
divided  into  party-coloured  sections  to  revolve  rapidly,  they 
produce  the  sensation  formed  by  a  blending  of  them  together; 
reel  and  blue,  for  example,  look  like  violet,  and  a  great 
variety  of  different  shades  produce  an  impression  as  of  gray. 
According  to  M.  Plateau,  the  duration  of  impressions  on  the 
retina  is  about  half  a  second. 

This  persistence  of  impressions  has  given  rise  to  the  con- 
struction of  an  apparatus,  which  is  at  the  same  time  an 
object  of  amusement  and  a  curious  philosophical  instrument. 
Such  is,  for  example,  the  phcnakistiscope.  It  was  upon  the 
same  principle  that  the  beautiful  experiments  were  founded, 
by  the  aid  of  which  Wheatstone  measured  the  duration  of 
lightning  flashes. 

Accidental  images. — We  may  compare  to  a  certain  extent 
the  action  of  light  on  the  retina  to  that  of  pressure  on  an 
elastic  surface.  When  the  rays  of  any  colour  strike  the 
retina,  it  resists  the  impulse  of  the  luminous  wave,  and 
strives  to  regain  a  state  of  repose.  When  the  action  of  light 
abruptly  ceases,  as  when  we  close  the  eyes,  for  example, 
after  a  very  short  time,  which  is  measured  by  the  duration  of 
the  impression  produced,  the  retina  returns  to  its  normal 
state  by  a  reaction  which  is  more  energetic  in  proportion  to 
the  length  or  duration  of  the  action.  It  passes  by  a  sort  of 
oscillation  from  the  condition  in  which  it  was  placed  by  the 


ACCIDENTAL    IMAGES.  175 

luminous  rays,  that  is  to  say,  from  the  positive  condition  of 
impression  to  a  negative  one,  and  then  forced  by  the  re- 
action, it  passes  the  point  of  repose,  and  recedes  in  an 
opposite  direction.  These  oscillations  continue  for  a  variable 
time,  growing  feebler  and  feebler.  The  reaction  of  the 
retina,  and  the  negative  phases  of  impression,  give  rise  to  a 
new  sensation  independent  of  any  external  agent,  by  pro- 
ducing what  are  termed  accidental  or  consecutive  images. 

We  know  that  two  colours  are  complementary  to  each 
other,  which  when  mingled  together  produce  white;  but  the 
accidental  images  have  the  peculiarity  of  presenting  them- 
selves in  the  colour  complementary  to  that  of  the  luminous 
rays  which  have  excited  the  retina;  thus,  if  we  look  steadily 
for  a  certain  length  of  time  in  a  very  clear  light  at  a  wall 
painted  red,  the  accidental  image  is  green,  and  if  the  wall  is 
orange,  the  image  will  be  blue,  &c. 

If,  on  going  into  a  dimly  lighted  gallery,  we  fix  our  eyes 
for  a  minute  or  two  on  a  window  which  receives  the  diffused 
light,  and  then  shut  them  suddenly  and  cover  them  so  as  to 
place  them  in  complete  darkness,  the  primitive  impression 
of  the  window,  with  the  panes  lighted  and  the  sashes  dark, 
remains  for  a  time,  but  very  soon  the  consecutive  image 
appears  with  the  frame  luminous  and  the  glass  obscure. 
This  last  image  will  appear  sooner  if  a  little  light  be  admitted 
through  the  closed  lids;  but  in  all  experiments  of  this  kind, 
the  eyeballs  must  be  kept  perfectly  still  under  the  veil  with 
which  they  are  covered,  for  the  slightest  change  in  the  direc- 
tion of  the  optic  axes  will  cause  the  images,  whether  primi- 
tive or  accidental,  immediately  to  disappear. 

One  of  the  most  important  facts  in  this  portion  of  the 
history  of  the  eye,  we  owe  to  the  observation  of  M.  Plateau. 
It  is  that  the  duration  of  the  uniform  intensity  of  the  retinal 
impression,  up  to  the  moment  when  it  begins  to  decrease,  is 
short  in  proportion  to  the  intensity,  that  is  in  proportion  as 
the  light  which  produced  it  was  brilliant  and  white ;  so  the 
impression  is  less  and  less  durable  in  its  first  intensity  ac- 
cording as  it  is  produced  by  looking  at  a  blue,  red,  yellow,  or 
white  disk;  if,  on  the  contrary,  we  measure  the  impression 
not  only  in  its  period  of  uniform  intensity,  but  from  its 


i76 


THE    HUMAN    BODY. 


maximum  to  its  minimum,  it  is  long  in  proportion  to  the 
brilliancy  of  the  light,  that  is  to  say,  as  the  disk  is  white, 
yellow,  red,  or  blue. 

Several  physiologists  explain  the  formation  of  accidental 
images  by  persistent  excitation  of  the  retina  with  diminution 
of  sensibility.  They  think  that  the  light  proper  of  the  retina 
plays  a  part  in  this  phenomenon. 


Fig.  41. — Irradiation. 

Irradiation,  accidental  fringes  of  light. — When  one  portion 
of  the  retina  is  excited  by  the  luminous  rays,  the  vibration 
is  extended  to  the  neighbouring  portions,  and  more  strongly 
in  proportion  as  the  light  is  white ;  the  result  of  this  is,  that 
of  two  objects  of  equal  dimensions  but  of  different  colour, 
the  lighter  one  in  colour  appears  the  larger  in  size.  If 
a  black  circle  is  traced  on  a  sheet  of  white  paper,  and  a 
white  circle  of  the  same  size  on  a  sheet  of  black  paper,  and 
both  placed  at  an  equal  distance  from  the  eye,  the  white  one 
appears  larger  than  the  black.  In  the  same  way,  if  we  make 
a  disk  half  white  and  half  black,  the  white  half  appears  the 
larger.  In  both  cases  the  white  encroaches  upon  the  black, 
because  the  impression  made  by  it  upon  the  retina  is  more 
vivid,  and  the  longer  the  experiment  is  continued  the  greater 
appears  the  difference  in  diameter.  The  name  of  irradiation 
has  been  given  to  the  group  of  phenomena  of  this  nature. 
It  is  the  same  cause  which  produces  a  ring  of  complementary 
colour  around  an  image  impressed  on  the  retina  by  a  coloured 
object.  If  a  square  of  red  be  placed  upon  a  white  ground, 


DALTONISM.       APPARENT    MOTION.  177 

and  the  eyes  are  fixed  upon  it  for  a  time,  a  border  of  pale 
green  forms  itself  round  the  red ;  and  in  the  same  way  a  yellow 
square  on  a  white  ground  produces  a  blueish  crown  round 
the  yellow  image:  these  are  called  accidental  fringes  of  light. 

M.  Chevreul  has  discovered  some  remarkable  laws  which 
govern  the  contrast  of  colours,  and  the  mutual  influence 
which  two  colours  placed  in  juxtaposition  have  upon  each 
other.  The  investigations  of  the  eminent  professor  are  not 
more  important  for  the  arts  than  for  science,  for  the  pheno- 
mena of  irradiation  are  produced  constantly  in  vision,  and 
artists  should  not  forget  them  for  a  moment  in  painting  or  in 
architecture.  It  is  unnecessary  to  remark  that  the  harmonious 
or  discordant  effect  produced  by  the  association  of  colours  in 
these  two  arts  is  of  the  utmost  importance,  and  although  in 
general  the  spectator  troubles  himself  very  little  about  the 
law  of  contrasts,  yet  he  is  notwithstanding  very  sensible  of 
the  impressions  which  result  from  its  observance. 

Daltonism — The  effects  of  a  disturbance  in  vision  described 
for  the  first  time  by  an  English  chemist  who  was  attacked 
by  it,  are  commonly  designated  by  this  term.  It  consists  of 
a  difficulty,  more  or  less  great,  of  distinguishing  colours,  some 
of  which  are  entirely  confounded  although  very  different,  as 
rose  and  gray,  red  and  green,  &c.  Very  marked  cases  of 
Daltonism  are  rarely  met  with,  but  in  a  slight  degree  the 
affection  is  not  uncommon. 

Apparent  motion  of  objects. — Among  the  most  common 
optical  illusions  we  may  cite  those  which  consist  of  the 
apparent  motion  of  external  objects.  When  on  a  boat,  for 
example,  or  in  a  carriage  which  is  in  motion,  we  seem  to  be 
at  rest  while  the  shore  or  the  sides  of  the  road  seem  to  be  in 
motion.  We  have  no  consciousness  of  the  movement  of 
external  objects  except  by  being  ourselves  at  rest,  and  when 
the  image  of  an  object  moves  across  the  retina  while  the  eye 
and  the  body  are  in  repose,  the  object  seems  to  change  its 
position  relative  to  us.  Carried  along  by  the  boat  or  carriage, 
without  our  bodies  taking  any  active  part  in  the  movement, 
we  judge  of  the  relative  displacement  instinctively,  and  from 
habit  we  refer  to  external  objects  the  movements  which  we 
d-^  not  ourselves  feel. 

12 


178  THE    HUMAN    BODY. 

Sometimes  there  is  an  apparent  displacement  of  objects, 
although  neither  the  objects  nor  the  eyes  are  in  motion,  but 
in  a  normal  condition  it  is  always  after  a  movement  of  the 
body  that  this  phenomenon  appears.  As  when  the  body  is 
whirled  round  rapidly  and  then  suddenly  stopped,  every- 
thing seems  to  turn  in  an  inverse  direction.  It  is  probable 
that  the  illusion  then  depends  on  the  impulse  to  movement 
in  a  certain  direction  imparted  to  the  brain;  in  fact,  if  we 
stop  after  turning  round,  the  sensation  of  turning  persists  for 
some  moments,  especially  in  the  head;  and  if  we  refer  it 
instinctively  to  external  objects,  it  is  in  consequence  both  of 
the  persistence  of  the  previous  sensation,  and  of  the  idea  of 
our  actual  immobility.  We  turn  still,  just  as  after  having 
laid  down  a  burden  we  continue  to  feel  its  weight  upon  us. 

Gratiolet  ascribes  the  apparent  motion  of  objects  under 
these  circumstances  to  insensible  oscillations,  which  displace 
to  a  limited  extent  the  ocular  axes,  but  he  does  not  indicate 
the  cause  of  these  oscillations. 

Optic  nerve. — The  visual  impressions  are  transmitted  from 
the  retina  to  the  brain  by  means  of  the  optic  nerve,  of  which 
that  membrane  appears  to  be  the  expansion.  The  two  optic 
nerves  converge  from  the  base  of  the  orbit  toward  the  centre 
of  the  base  of  the  skull,  where  there  is  an  interlacement  of 
their  fibres  in  such  a  manner,  that  a  portion  of  the  right 
nerve  goes  to  the  left  side  of  the  brain,  and  a  part  of  the  left 
nerve  to  the  right  side;  this  is  called  the  chiasma,  or  commis- 
sure of  the  optic  nerves.  Physiological  theories,  which  are 
no  longer  tenable,  have  been  deduced  from  this  crossing  of 
the  nerves,  and  nothing  positive  is  yet  known  of  the  relation 
between  this  disposition  and  the  visual  function.  Mechani- 
cal irritation  of  the  nerve  seems  to  develop  luminous  impres- 
sions as  in  the  retina,  but  it  causes  no  pain  whatever. 

Movements  of  the  eye. — The  ocular  globe  is  put  in  motion 
in  the  orbit  by  six  muscles,  grouped  two  by  two,  which  raise 
or  lower  the  eye,  turn  it  inward  or  outward,  or  on  its  antero- 
posterior  axis.  In  these  movements  the  centre  of  the 
globe  is  immovable,  and  the  eye  moves  around  its  transverse 
and  vertical  diameters.  These,  three  orders  of  movements 
are  independent  of  each  other,  and  may  be  made  singly,  or  in 


MOVEMENTS    OF    EYE.       RANGE    OF    VISION.  179 

combination,  in  such  a  manner  as  to  direct  the  pupil  towards 
all  points  of  the  circumference  of  the  orbit.  The  straight,  supe- 
rior, inferior,  external,  and  internal  muscles  move  it  upward, 
downward,  inward,  and  outward,  and  their  successive  action 
gives  it  a  movement  of  circumduction.  The  two  oblique 
muscles  turn  the  eye  on  its  antero-posterior  axis,  in  such  a 
manner  as  always  to  maintain  the  horizontal  position  of  its 
transverse  diameter,  when  the  head  or  the  body  inclines  to 
the  right  or  the  left.  All  these  muscles  take  a  direct  or  indi- 
rect part  in  every  movement  of  the  eye;  if  looking  up  or  down, 
for  example,  the  straight,  superior,  or  inferior  acts  alone ;  the 
other  muscles  assure  the  movement,  and  confine  it  to  the 
transverse  axis.  Such  is  the  perfection  of  this  mechanism, 
that  the  cornea  is  raised  or  lowered  without  the  least  lateral 
deviation,  like  the  objective  of  a  meridian  glass;  and  the  eye 
perceives  by  this  succession  of  movements  if  the  image  of  a 
line  on  the  retina  deviates  o '00002  of  an  inch  from  the 
vertical. 

The  eyelids  follow  the  movements  of  the  globe  when  it  is 
raised  or  lowered,  obeying  the  action  of  the  muscles  of  which 
they  receive  the  aponeurotic  prolongations. 

The  movements  of  the  two  eyes  are  always  symmetrical, 
and  of  the  same  kind;  both  are  raised  or  lowered  at  once, 
directed  to  right  or  left,  or  around  their  axes;  they  can  be 
turned  inwards  simultaneously  to  see  an  object  very  near  at 
hand,  or  slightly  outwards,  when  they  turn  from  such  a  point 
to  one  in  the  distance.  Even  when  one  eye  is  closed,  the 
globe  turns  in  the  same  direction  as  that  of  the  open  eye. 
This  unity  and  variety  of  movement  contribute  to  make  the 
eye  the  most  important  feature  of  the  physiognomy. 

Extent  and  delicacy '  of  vision. — As  regards  the  distance  at 
which  man  can  distinguish  objects,  he  is  less  gifted  than 
many  other  animals;  but  in  every  other  respect  his  visual 
powers  are  at  least  equal  to  that  of  inferior  beings.  We  know 
very  little  of  the  sensations  produced  in  animals  by  colours; 
it  seems  probable  that  they  have  a  relative  perception  of 
them  to  a  certain  extent,  as  the  sight  of  red  irritates  the  bull, 
for  example;  and  we  know  that  birds  of  prey  from  a  great 
height  in  the  air  distinguish  the  colour  as  well  as  the  form  of 


I  So  THE    HUMAN    BODY. 

a  lark  or  a  quail  hiding  in  the  ploughed  fields,  although  it  so 
closely  resembles  that  of  the  soil.  But  if  we  should  suppose 
them  endowed  with  sensitive  faculties,  useless  within  the 
limits  of  their  instinct,  could  we  find  anything  in  animals 
more  perfect  than  the  organs  to  which  man  owes  the  prodi- 
gies of  painting?  We  must,  however,  distinguish  here  between 
that  which  pertains  to  the  visual  apparatus,  and  that  which 
proceeds  from  the  intellect.  The  eye  perceives  the  tints 
which  nature  offers  in  almost  infinite  variety;  the  mind  com- 
pares them,  and  recognizes  the  elementary  colours  of  which 
they  are  composed;  the  eye  reflects  in  turn  the  model,  the 
palette,  and  the  picture;  the  mind  perceives  the  relation  of 
shades,  and  combines  them  in  such  a  manner,  that  by 
mingling  or  contrasting  them  such  a  result  is  produced  as 
conforms  to  the  first  impression;  but  in  order  that  an  artist 
may  judge  whether  red  or  blue  predominates  in  a  violet  tint, 
in  order  to  appreciate  the  shade,  the  retina  must  transmit  it 
to  the  brain  in  its  purity. 

At  the  manufactory  of  the  Gobelins,  we  see  the  wools  used 
in  the  fabrication  of  the  tapestries  arranged  according  to  their 
shades.  The  number  of  these  shades  exceeds  28,000,  and 
yet  when  we  compare  two  approximate  shades  we  distinguish 
them  with  facility,  and  perceive  the  interval  which  separates 
them. 

The  people  who  live  in  the  country,  seamen,  and  especially 
men  living  in  a  savage  state,  generally  have  sharper  sight 
than  the  residents  of  cities.  May  not  the  habit  of  seeking  to 
distinguish  objects  at  a  distance  give  the  eyes  a  power  which 
is  not  acquired  when  they  always  act  within  a  limited  hori- 
zon? Without  assimilating  exactly  the  effects  of  exercise  on 
the  eye  to  those  which  result  from  exercise  of  a  muscle,  we 
are  justified  in  thinking  that  an  almost  incessant  accommo- 
dation to  great  distances  must  influence  the  eye  in  that 
respect,  and  if,  as  is  very  probable,  the  accommodation  takes 
place  by  the  contraction  of  muscular  fibres,  the  explanation 
of  the  increased  range  of  the  eye  from  exercise  is  very  simple; 
but  facts  are  wanting  which  verify  and  measure  this  increase 
in  individuals.  There  is  no  doubt,  however,  that  men  from 
whom  the  horizon  is  habitually  distant  distinguish  certain 


RANGE    OF   SIGHT.  l8l 

objects  at  a  point  where  they  are  confused  to  other  persons, 
although  within  the  reach  of  their  vision. 

A  ship  appears  on  the  horizon,  a  man  unacquainted  with 
the  sea  can  hardly  distinguish  the  sails  of  this  white  cloud 
springing  from  the  waters;  but  a  sailor  will  tell  you  that  is  a 
brig  or  a  three-master,  a  war  vessel  or  a  merchant  ship,  and 
often  he  will  even  come  at  its  tonnage,  its  lading,  its  nation- 
ality, and  its  name.  The  Arab  and  the  European  in  the 
midst  of  the  sands  of  Sahara  see  on  the  horizon  an  object, 
which  to  the  European  is  only  a  black  point  without  appre- 
ciable form ;  the  Arab  sees  a  camel  distinctly,  and  declares 
that  it  is  at  such  or  such  a  distance,  without  ever  being  de- 
ceived. 

The  inexperienced  mountain  traveller  sees  before  him  a 
chaos  of  slopes  and  abrupt  walls,  of  elevations  and  windings, 
among  whicn  he  can  distinguish  neither  route  nor  practicable 
passage;  but  the  mountaineer  sees  at  once  the  accessible 
points,  and  the  turns  which  he  must  take  to  reach  the  summit 
of  the  apparently  impassable  barrier.  This  proves  not  that 
the  sailor,  the  mountaineer,  or  the  Arab  have  sharper  sight 
than  the  stranger  to  their  country;  but  that  they  have  learned 
to  know  the  signification  of  such  and  such  details  of  form, 
such  a  particularity  of  colour  and  the  like,  which  are  for  them 
distinguishing  marks,  which  seem  to  trace  before  their  eyes 
the  description  which  they  give  to  their  fellow-voyager  of 
objects  that  are  either  confused  or  imperceptible  to  him.  It 
is  therefore  to  acquired  notions,  and  skill  in  seeing  objects, 
rather  than  to  extent  of  vision,  that  they  owe  the  faculty  of 
distinguishing  objects  at  great  distances. 

We  find  also  in  all  countries,  and  in  all  climates,  men  who 
have  extraordinary  powers  of  vision.  Wrangel  speaks  in  his 
voyage  to  the  Polar  seas,  of  a  Yakoute  who  related  having 
seen  a  great  star  swallow  little  ones,  and  then  vomit  them  up 
again.  That  man,  says  Wrangel,  had  seen  the  eclipses  of 
the  satellites  of  Jupiter.  Humboldt  tells,  in  his  Cosmos,  of  a 
tailor  in  Breslau,  named  Schcen,  who  also  had  seen  the 
satellites  of  Jupiter  with  the  naked  eye.  No  examples  of  a 
greater  range  of  vision  are  known. 


CHAPTER  XII. 


Sense  oj  hearing. — Organ  of  hearing.— External  ear;  pavilion  of  the 
ear,  auditory  canal. — Middle  ear;  tympanum,  drum,  or  membrana 
tympani,  fenestra  ovalis,  fenestra  rotunda,  Enstachian  tube,  the  small 
bones  of  the  ear,  muscles  and  movements  of  the  small  bones. — Internal 
ear;  labyrinth,  vestibule,  semicircular  canals,  cochlea,  membranous 
labyrinth. — Auditory  nerve. — Noises  and  sounds;  duration,  pitch,  in- 
tensity and  quality  of  sound;  passage  of  sound  through  air,  water,  solid 
bodies;  gravity,  sharpness  of  sound. — Mechanism  of  hearing ;  functions 
of  different  parts  of  the  ear;  movement  of  sounds  in  the  ear;  propagation 
of  sounds  to  the  audilory  apparatus  by  the  vibrations  of  the  bones  of  the 
skull.  —  Opinions  of  physiologists  on  the  functions  of  different  portions  of 
the  labyrinth;  theory  of  llelmholtz. — Fineness  and  delicacy  of  hearing. — 
Correctness  of  the  ear.  — Estimation  of  the  intensity,  the  distance,  and 
the  direction  of  sounds;  ventriloquism. — Duration  of  auditory  impres- 
sions.— Sensations  having  an  internal  origin. — Parallel  between  the 
eye  and  ear. 


The  ear. — The  organ  of  hearing  is  not  placed  on  the  face, 
like  those  of  sight,  smell,  and  taste;  but  in  the  thickness  of 
the  base  of  the  skull.  But  we  may  say  it  belongs  to  the  face 
as  one  of  the  elements  of  the  physiognomy,  by  its  external 
apparatus,  which  contributes  to  the  expression  of  the  head. 
The  ear  is  divided  anatomically  into  three  regions — the  exter- 
nal, middle,  and  internal  ear. 

External  ear. — This  is  the  least  complicated  portion  of  the 
organ;  it  is  composed  of  the  pavilion,  or  projecting  part,  and 
the  auditory  canal. 

T}\e  pavilion  of  the  ear  is  similar,  as  the  name  implies,  to 
the  open  portion  of  wind-instruments  or  a  speaking-trumpet. 
It  is  an  acoustic  horn,  which  gathers  the  sonorous  waves,  and 
conducts  them  to  the  intricacies  of  the  auditory  apparatus. 
It  consists  of  an  elastic  cartilaginous  layer  covered  with  a 


EXTERNAL   EAR. 


delicate  skin,  and  is  curiously  modelled.  Its  border,  rounded 
in  its  upper  portion,  and  folded  back  on  itself,  forms  the 
rim  or  helix,  and  terminates  at  the  lower  portion  in  the  lobe. 
The  concha  is  in  the  centre,  and  is  bounded  behind  by  the 


Fig.  42. — Section  showing  the  different  parts  of  the  ear. 


A.  Pavilion,  or  projecting  ear. 

B.  External  a^^ditory  canal. 

C.  Meinbrana  tympani. 
I).  Tympanum. 

E.  Incus,  or  anvil. 


M.  Malleus,  or  hammer. 
G.  Semicircular  canal. 
H.  Cochlea,  or  shell. 
I.  Ettstachian  tube. 


antihelix,  and  terminates  in  the  auditory  canal.  The  pro- 
jections of  the  tragus  and  antitragus,  separated  by  an  ellip- 
tical slope,  protect  the  orifice  of  this  canal,  and  a  down, 
which  might  be  called  the  lashes  of  the  ear,  sifts  the  air  as  it 
passes  into  the  organ. 

The  pavilion  of  the  ear  is  directed  forward,  projects  from 
the  head,  and  its  lines  are  in  beautiful  harmony  with  the  oval 
of  the  face. 


184  THE    HUMAN    BODY. 

De  Blainville  compares  the  curves  and  the  surface  of  the 
pavilion  of  the  ear  to  those  of  the  head.  According  to  this 
naturalist  the  curve  of  the  superior  portion  of  the  pavilion 
corresponds  to  that  of  the  cranium,  and  the  free  border  of 
the  rim  describes  a  curve  parallel  to  that  which  marks  the 
temporal  fossa.  When  the  head  is  not  prominent  .in  its 
middle  region,  and  the  temporal  fossae  are  slightly  marked,  "• 
the  rim  is  absent;  it  is,  on  the  contrary,  broad  and  prominent 
when  the  arch  of  the  skull  overhangs  the  temporal  fossae. 
The  concha  corresponds  to  the  upper  jaw,  and  is  propor- 
tional to  it;  and  the  prominence  of  the  origin  of  the  helix 
represents  that  of  the  zygomatic  arch;  and  lastly,  the  profile 
of  the  lobe  is  like  that  of  the  upper  jaw.  It  is  remarkable 
that  this  lobe  exists  only  in  man,  and  that  man  only  has  also 
a  prominent  and  angular  chin. 

The  auditory  canal,  which  represents  the  tube  of  the  acoustic 
trumpet  formed  by  the  external  ear,  is  cartilaginous  next  the 
concha,  and  the  remaining  part  is  excavated  in  the  petrous 
or  stony  portion  of  the  temporal  bone.  This  canal  is  about 
one  and  a  fifth  inch  in  length,  and  its  entire  disposition  is  such 
that  foreign  bodies  suspended  in  the  air  cannot  pass  with  it 
to  the  membrana  tympani.  It  is  bent  near  the  concha  in 
such  a  manner  that  the  air,  in  transmitting  sound  to  the  middle 
ear,  does  not  penetrate  in  right  lines,  thus  protecting  the 
sensibility  of  the  membrane. 

The  middle  ear. — The  membrana  tympani  (membrane  of 
the  drum),  of  which  the  name  indicates  the  function,  is  a 
membranous  partition  stretched  obliquely  across  the  bottom 
of  the  auditory  canal,  which  it  separates  from  the  middle  ear 
or  drum.  This  membrane  is  semi-transparent  and  very  thin, 
although  it  is  composed  of  three  layers;  it  vibrates  under  the 
impression  of  the  sonorous  waves,  and  transmits  the  vibratory 
movement  to  the  little  bones  of  the  ear.  Between  the 
membrana  tympani  and  the  internal  ear  is  the  drum  or  the 
tympanum,  a  cavity  hollowed  out,  like  all  those  of  the  middle 
and  internal  ear,  in  the  petrous  portion  of  the  bone.  Among 
the  details  of  its  form  and  organization,  we  remark  the 
fenestra  ovalis,  which  communicates  with  the  vestibule,  and 
\\\zfenestra  rotunda,  which  leads  to  the  cochlea.  The  drum 


SMALL  BONES  OF  EAR.   INTERNAL  EAR.       185 

also  communicates  with  the  mastoid  cells,  numerous  sinuses 
which  are  found  in  the  mastoid  process  of  the  temporal  bone, 
containing  air,  and  designed  to  multiply  the  vibratory  surfaces; 
and  lastly,  it  unites  by  a  sort  of  funnel  with  the  Eustachian 
tube,  a  canal  about  one  inch  and  a  third  in  length,  which 
opens  into  the  upper  portion  of  the  pharynx,  and  admits  the 
air  into  the  middle  ear. 

The  ossicles  or  small  bones  of  the  ear. — These  are  four  in 
number;  they  are  articulated  together,  and  form  a  bony 
chain  which  runs  from  the  membrana  tympani  to  the  fenestra 
ovalis,  following  a  broken  line.  They  have  been  named  the 
hammer  (malleus),  the  anvil  (incus),  the  lenticular\)QK<t,  and  the 
stirrup  (stapes),  from  their  form  or  their  functions.  Special 
muscles  act  upon  the  malleus  and  the  stapes,  which  are  at 
the  two  extremities  of  the  chain ;  the  incus  and  the  lenticular 
bone  serving  as  media  for  the  propagation  of  the  vibrations. 
The  motion  impressed  upon  one  of  these  extremities  is  com- 
municated to  the  other  by  a  sort  of  see-saw  movement  of  the 
little  bones,  the  mechanism  of  which  is  pretty  nearly  repre- 
sented by  that  of  a  bell.  One  extremity  of  the  hammer,  the 
handle,  is  fitted  into  the  membrane  of  the  tympanum,  and 
when  the  muscle  of  the  hammer  contracts,  the  membrane 
tightens,  a  phenomenon  which  will  be  discussed  further  on. 
The  muscle  of  the  stirrup  attaches  the  flat  part  of  this  bone 
to  the  fenestra  ovalis,  and  according  to  M.  Longet  prevents 
it  from  being  forced  in  a  contrary  direction  under  the  influ- 
ence of  the  muscle  of  the  hammer,  of  which  it  is  the  an- 
tagonist. 

Labyrinth  or  internal  ear. — The  internal  ear  is  that  por- 
tion of  the  organ  of  hearing  which  perceives  the  impression 
of  sound,  and  transmits  it  directly  to  the  brain.  It  is  hollowed 
out  in  the  petrous  bone,  and  is  divided  naturally  into  three 
distinct  compartments,  named  the  vestibule,  the  semicircular 
canals,  and  the  cochlea  or  snail-shell.  These  divisions  form 
together  one  of  the  most  complex  and  delicate  pieces  of  me- 
chanism in  the  human  body. 

The  labyrinth  is  composed  of  a  bony  cavity  which  incloses 
a  membranous  cavity  in  a  portion  of  its  space,  and  from  this 
circumstance  arises  the  distinction  made  by  anatomists 


1 86  THE    HUMAN    BODY. 

between  the  osseous  and  membranous  labyrinths.  We  shall 
first  consider  the  osseous  labyrinth. 

The  vestibule  is  an  ovoid  cavity  placed  in  the  centre  of  the 
internal  ear,  between  the  semicircular  canals  and  the  cochlea. 
It  communicates  with  the  drum  by  the  fenestra  ovalis,  which 
is  closed  by  the  base  of  the  stapes.  In  it  are  seen  the  open- 
ings of  the  five  semicircular  canals,  of  the  vestibular  stair  of 
the  cochlea,  and  of  the  vestibular  canal.  This  latter  is  the 
opening  of  a  vascular  canal  which  traverses  the  petrous  bone. 

Semicircular  canals.  —  This  is  the  name  given  to  three 
curved  tubes  forming  axes  of  circles,  one  which  is  horizontal 
and  is  placed  between  the  two  others,  which  are  vertical. 
They  are  each  enlarged  into  a  bulbous  cavity  (ampulla)  at 
one  extremity,  and  communicate  with  the  vestibule  by  five 
orifices. 

Cochlea  (or  snail-shell). — This  is  the  name  given  to  a 
conoid  cavity  which  is  separated  from  the  semicircular 
canals  by  the  vestibule,  with  which  it  communicates,  and 
terminates  at  the  fenestra  rotunda.  The  cavity  of  the  cochlea 
is  a  spiral,  describing  two  turns  and  a  half  round  its  columella 
or  axis;  it  is  divided  transversely  into  two  portions  by  a 
partition — -the  lamina  spiralis,  throughout  its  entire  length. 
That  portion  opening  into  the  vestibule  is  called  the  scala 
vestibuli;  and  that  opening  into  the  fenestra  rotunda  the 
scala  tympani — by  which  it  would,  if  it  were  not  for  the 
membrane  which  closes  it,  communicate  with  the  cavity  of 
the  tympanum. 

The  lamina  spiralis  is  divided  lengthwise  into  a  bony  por- 
tion, which  corresponds  at  its  internal  border  to  the  axis; 
and  a  membranous  portion,  which  attaches  the  osseous  por- 
tion to  the  external  wall  of  the  cochlea.  This  wall  is  formed 
by  the  spiral  plate.  The  cochlea  is  lined  by  a  fibro-mucous 
membrane,  which  appears  to  be  a  continuation  of  the  perios- 
teum of  the  other  two  cavities  of  the  labyrinth;  the  mem- 
branous portion  of  the  spiral  plate  may  be  considered  as  a 
prolongation  of  the  membranous  labyrinth.  Lastly,  the 
vascular  canal,  called  the  canal  of  the  cochlea,  analogous  to 
that  of  the  vestibule,  communicates  also  with  the  cavity  of 
the  skull.  The  base  of  the  cochlea  rests  on  the  bottom  of 


MEMBRANOUS    LABYRINTH.       AUDITORY    NERVE.  187 

the  internal  auditory  canal,  by  which  the  auditory  nerve 
enters  the  organ  of  hearing. 

Mffttbranous  labyrinth. — -The  bony  walls  of  the  vestibule 
and  of  the  semicircular  canals  inclose  and  protect  a  mem- 
branous apparatus  of  the  same  form,  which  is  separated  from 
them  by  a  space  filled  with  a  limpid  fluid  vd\\z&  perilymp/i  or 
liquor  Cotunnii.  The  membranous  labyrinth  is  therefore 
smaller  in  proportion  than  the  osseous ;  the  difference  in  size 
is  about  one-half.  Its  cavities  contain  a  fluid  analogous  to 
the  perilymph,  and  which  De  Blainville  has  compared  to  the 
vitreous  humor  of  the  eye;  they  also  contain  semi-transparent 
tubes  and  membranous  sacs,  the  appearance  of  which  is 
closely  analogous  to  that  of  the  retina.  The  membranous 
vestibule  is  composed  of  two  distinct  parts,  the  saccule  and 
utricle,  in  which  there  exists  a  calcareous  dust,  which  appears 
to  represent  in  man  and  the  mammifera  the  auditory  stones 
or  otoliths  of  fishes. 

Auditory  nerve. — The  auditory  or  acoustic  nerve  specially 
belongs  to  the  organ  of  hearing,  and  is  remarkable  for  the 
softness  of  its  texture:  it  enters  the  ear  by  the  internal 
auditory  canal,  and  divides  into  two  branches,  one  of  which 
distributes  itself  to  the  vestibule  and  to  the  ampullar  extremi- 
ties of  the  semi-circular  canals;  the  other  goes  to  the  cochlea, 
and  has  been  called  the  cochlear  branch.  Its  ramifications 
are  extremely  minute;  they  line  the  surface  of  the  modiolus 
and  spread  themselves  regularly  over  the  spiral  plate,  dimin- 
ishing in  length  from  the  base  to  the  summit  in  such  a  manner 
that  if  we  suppose  the  spiral  plate  to  be  placed  upright,  and 
forming  a  triangular  plane,  these  filaments  would  resemble 
the  strings  of  a  harp — the  longest  at  the  base  of  the  triangle 
and  the  shortest  at  the  summit.  They  are  called  the  fibres  of 
Corti,  from  the  anatomist  who  first  described  them.  The 
microscope  enables  us  to  count  more  than  three  thousand, 
and  we  shall  see  later  the  part  they  are  supposed  to  fill  in 
audition. 

But  before  opening  the  physiological  question,  we  will 
notice  summarily  some  of  the  phenomena,  the  existence  of 
which  is  revealed  to  us  by  the  ear. 

Noises  arid  sounds.  —  Physicists  divide  sounds  into  two 


1 88  THE    HUMAN    BODY. 

classes — musical  sound  and  noise.  They  both  have  the  same 
origin,  the  vibrations  of  a  body  transmitted  to  the  air.  The 
short  duration  of  a  noise,  and  the  lack  of  isochronism  in  its 
vibrations,  do  not  permit  us  to  appreciate  its  musical  value, 
and  this  distinguishes  it  from  musical  sound.  Thus  the  ex- 
plosion of  gas  or  powder,  the  crack  of  a  whip,  or  the 
breaking  of  a  branch  make  a  noise,  but  give  no  musical 
sound.  The  limit  between  sound  and  noise  is  otherwise  in- 
sensible, and  varies  according  to  the  individual.  A  noise  as 
well  as  a  sound  may  be  grave  or  acute,  feeble  or  intense. 
The  difference  in  the  duration  of  the  sensation  does  not 
permit  us  to  compare  noise  to  sound,  but  yet  the  ear  seizes 
the  relation  between  two  noises  as  well  as  between  two 
musical  sounds. 

A  sound  is  called  musical  when  its  pitch  can  be  estimated 
absolutely  and  relatively  to  other  sounds  grave  or  acute;  or, 
in  other  words,  when  the  number  of  vibrations  follows  a 
constant  law  and  can  be  determined. 

Whatever  may  be  the  difference,  however,  between  a  noise 
and  a  musical  sound,  the  one  is  only  a  variety  or  degree  of 
the  other,  and  both,  proceeding  from  the  same  source,  may 
be  studied  under  the  generic  denomination  of  sound. 

Sound  has  four  fundamental  properties — duration,  pitch, 
intensity,  and  timbre  or  distinctive  quality.  The  three  first 
named  are  defined  by  the  words  which  express  them:  as 
for  the  timbre,  it  is  the  resonance  peculiar  to  each  instru- 
ment, to  each  voice,  which  enables  us  to  distinguish  without 
difficulty  the  notes  of  a  violin,  a  clarionette,  or  a  flute,  and 
to  recognize  individuals  by  hearing  them  speak  or  sing. 

The  duration  of  a  sound  is  measured  by  the  time  that  the 
body  vibrates  from  which  it  proceeds ;  it  is  high  and  acute 
according  to  the  number  of  vibrations,  and  its  intensity  is 
measured  by  the  amplitude  or  range  of  the  vibrations  which 
cause  it,  and  this  amplitude  is  in  proportion  to  the  force 
acting  on  the  sonorous  body. 

The  "timbre"  of  sounds  was  long  an  insoluble  enigma  to 
the  physicist. and  the  physiologist.  |.  Miiller  had  suspected 
its  origin  in  attributing  it  either  to  the  isochronism  of 
sonorous  waves  of  different  velocity,  or  to  waves'  of  different 


TIMBRE.   SPEED  OF  SOUND.  189 

length,  producing  a  compound  wave  of  a  peculiar  form, 
or  else  to  a  longitudinal  vibration  in  the  sonorous  body 
taking  place  at  the  same  time  as  the  transverse  vibration. 
M.  Longet  states,  with  greater  precision,  that  the  timbre 
of  the  human  voice,  and  of  wind-instruments,  results  from 
the  co -existence  of  several  sonorous  waves  of  different 
tone  and  intensity,  which  modify  the  general  form  of  the 
principal  wave.  But  at  last  the  beautiful  experiments  of 
M.  Helmholtz  have  demonstrated,  that  the  timbre  of  a  sound 
depends  upon  the  number  of  the  harmonic  notes  which  are 
produced  at  the  same  time  as  the  fundamental  note,  and 
upon  their  relative  intensity. 

When  a  cord  of  a  piano  giving  the  C,  for  example,  is 
struck,  that  note  is  heard,  but  a  little  attention  enables  the 
ear  to  hear  other  simultaneous  and  weaker  sounds;  they  are 
the  result  of  partial  vibrations  which  take  place  in  the  length 
of  the  cord,  according  to  certain  laws  which  cannot  be  ex- 
plained here.  The  C  given  by  the  shock  impressed  on 
the  cord  is  the  fundamental  note,  the  other  notes  which  are 
superposed  upon  it  are  the  harmonics.  From  their  fusion 
with  the  fundamental  note,  there  results  to  the  ear  a  complex 
sound  which  it  decomposes  instinctively  into  simple  sounds, 
but  they  cause  only  a  single  sensation  in  the  brain,  that  of 
a  C  having  a  special  timbre.  Whether  the  fundamental 
note  be  given  by  an  instrument  or  by  the  human  voice, 
the  same  phenomena  are  produced,  and  the  timbre  proves 
equally  characteristic  to  the  ear.  The  timbre  is  therefore 
the  distinctive  quality  of  the  sonorous  body — the  form,  in  a 
certain  sense,  of  sounds. 

Sound  moves  more  rapidly  in  warm  air  than  in  cold;  its 
velocity  in  the  atmosphere  is  1 1 18*45  ^ee^  m  a  second  at  16°  C. 
(60 '8°  F.)  or  1 086 '3 7  feet  at  zero,  according  to  experiments 
made  by  the  Bureau  of  Longitudes  in  1822;  and  according 
to  those  of  Bravais  and  Martins  made  in  1844,  it  is  1092*89 
feet  at  zero  (Cent.)  This  velocity  is  not  modified  by  the  varia- 
tions in  the  pressure  of  the  atmosphere,  and  it  is  the  same 
whether  in  a  horizontal,  vertical,  or  oblique  direction.  It  is 
increased  or  diminished  by  the  wind,  according  as  it  blows 
in  the  direction  of  the  sound  or  contrary  to  it,  though  the 


190  THE    HUMAN    BODY. 

velocity  is  not  changed  if  the  wind  blows  perpendicularly  to 
this  direction.  Sound  cannot  be  produced  in  a  vacuum,  and 
it  is  therefore  less  intense  in  proportion  as  the  air  is  more 
rarefied.  It  is  weaker,  for  instance,  on  the  tops  of  high 
mountains  than  in  the  lower  strata  of  the  atmosphere, 
although  the  profound  silence  which  reigns  at  times  in  these 
elevated  regions  permits  even  very  feeble  sounds  to  be 
heard  at  great  distances.  We  were  enabled  to  prove  this 
with  M.  Martins  in  1844.  Near  St.  Cheron  (Seine-et-Oise), 
at  an  elevation  of  459  feet,  a  diapason  placed  on  a  drum 
could  be  heard  in  the  daytime  277  yards  off;  while  on  the 
great  plateau  of  Mont  Blanc,  at  a  height  of  13,123  feet, 
the  sound  of  the  same  instrument  could  be  heard  at  a 
distance  of  368  yards.  On  the  top  of  Mont  Blanc,  we 
could  hear  our  guides  talk  at  a  distance  of  437  yards,  and 
they  could  hear  us  speak  also. 

Humboldt  observes  that  sound  is  more  intense  and  is 
propagated  farther  in  the  night  than  in  the  daytime,  in  spite 
of  the  noises  and  of  the  wind  which  in  tropical  countries 
increase  after  sunset.  This  diminution  in  sounds  during  the 
day  is  attributed  by  the  illustrious  observer  to  the  unequal 
temperature  of  the  strata  of  the  atmosphere,  under  the  influ- 
ence of  the  sun  and  the  radiation  from  the  earth. 

Sound  moves  much  more  quickly  in  water  and  in  solid 
bodies  than  in  the  air.  Colladon  and  Sturm  found  its 
velocity  to  be  4708  feet  in  a  second  in  the  waters  of  the 
Lake  of  Geneva  at  8°  C.  (46*4°  F.)  of  temperature;  according 
to  the  experiments  of  Biot,  its  average  velocity  is  10,663  ^eet 
in  cast-iron  pipes.  This  is  about  five  times  greater  in  water 
than  in  air,  and  nine  times  greater  in  the  pipe. 

Humboldt  records  that  sometimes  volcanic  detonations 
have  been  transmitted  through  the  earth  a  distance  of  500  to 
745  miles. 

It  is  stated  that  the  gravest  sound  which  can  be  perceived 
by  the  ear  is  32  vibrations  in  a  second  (16  according  to 
Savart),  and  the  most  acute,  according  to  Despretz,  is  73,700 
vibrations.  A  sound  of  60,000  vibrations  is,  according  to 
M.  Martins,  very  feeble,  difficult  to  hear,  and  of  such  sharp- 
ness as  to  cause  a  painful  impression  on  the  ear.  The 


MECHANISM    OF    HEARING.  IQI 

sounds  which  are  easily  perceived  and  appreciated  by  the 
ear  vary  from  100  to  2000  vibrations.  The  gravest  C  of 
a  piano  of  six  octaves  and  a  half  counts  128,  and  the  most 
acute  8192. 

Mechanism  of  hearing. — The  sonorous  waves  penetrate 
directly  into  the  auditory  canal,  or  after  they  have  en- 
countered the  outer  portion  of  the  ear,  the  sinuosities  of 
which  they  follow,  and  the  ear  itself  vibrates  to  the  shock  of 
sounds,  and  these  vibrations  are  transmitted  gradually  to  the 
organ.  Savart,  who  has  demonstrated  this  phenomenon  by 
experiments,  observes  that  the  very  irregular  surface  of  the 
ear  always  presents  some  portion  at  an  angle  most  favourable 
to  the  sonorous  waves,  whatever  may  be  their  direction ;  in 
fact,  the  force  with  which  they  act  upon  its  walls  is  in  direct 
proportion  to  their  approach  to  the  perpendicular. 

If,  for  example,  the  pavilion  of  the  right  ear  be  covered 
with  some  substance  which  obliterates  all  the  inequalities 
and  transforms  it  into  a  plane  surface,  a  sound  cannot  be 
heard  on  that  side  so  well  as  on  the  left,  when  produced  at 
an  equal  distance  from  both  ears.  It  is  to  be  presumed, 
also,  that  the  pavilion,  which  increases  all  sounds  equally, 
does  not  vibrate  in  unison  with  any  one  sound,  nor  has  it, 
owing  to  the  irregularities  of  its  surface,  any  one  peculiar  to 
itself.  And  finally,  the  form  of  the  pavilion,  and  its  inclina- 
tion in  relation  to  the  head,  seem  to  have  a  certain  influence 
on  the  acuteness  of  hearing. 

Besides  the  vibrations  which  enter  directly  into  the  audi- 
tory canal,  and  those  which  come  from  the  pavilion,  this 
canal  receives  also  those  of  the  bones  of  the  cranium  and 
transmits  them  to  the  tympanum.  These  last  and  those  of 
the  pavilion  reach  the  tympanum  sooner  than  the  first,  for 
the  reason  already  stated,  that  sounds  move  more  rapidly  in 
fluids  and  solids  than  in  the  atmosphere.  It  receives  there- 
fore two  orders  of  vibrations,  but  in  passing  to  this  membrane 
the  vibrations  of  the  air  are  transformed  into  those  of  a  solid 
body;  from  which  we  may  conclude  with  Savart  and  Miiller, 
that  the  function  of  the  tympanum  is  to  serve  as  a  medium 
between  the  air  and  the  small  bones  of  the  ear,  by  changing, 
as  we  have  just  seen,  the  atmospheric  vibrations. 


192  THE    HUMAN    BODY. 

Sounds,  augmented  by  the  external  ear,  and  concentrated 
upon  the  tympanum,  are  transmitted  to  the  little  bones, 
and  again  augmented  during  this  transit,  by  a  more  close 
concentration  upon  the  base  of  the  stapes. 

We  have  seen  that  the  contraction  of  the  muscle  of  the 
hammer  causes  tension  of  the  tympanum.  This  membrane 
then  passes  from  a  state  of  repose  to  a  variable  degree  of 
tension,  upon  the  effects  of  which  physiologists  are  not 
agreed.  According  to  Bichat,  it  is  more  tense  in  proportion 
to  the  feebleness  of  the  sounds,  and  to  the  greater  necessity 
of  action  of  the  organ  in  order  to  perceive  them.  Accord- 
ing to  Miiller  and  Savart,  the  tension  protects  the  organ 
of  hearing  against  too  violent  sounds  by  lessening  the  con- 
ducting power  of  the  tympanum.  According  to  Longet, 
the  muscle  of  the  malleus  has  no  other  function  than  to 
obviate  variations  in  the  tension,  and  especially  to  prevent 
the  entire  relaxation  of  the  membrane;  in  a  word,  it  is  the 
key  of  the  tympanum. 

The  sonorous  waves  traverse  the  chain  of  little  bones,  and 
are  transmitted  by  it  to  the  fluid  in  the  labyrinth,  thus 
changing  their  medium  without  losing  their  intensity.  If  the 
little  bones  were  articulated  in  such  a  manner  as  to  form  a 
rigid  straight  line,  instead  of  an  elastic  broken  one,  the  dis- 
tance between  the  tympanum  and  the  fenestra  ovalis  being 
susceptible  to  variation,  the  result  would  be  that  in  certain 
cases  the  pressure  on  the  tympanum  and  on  the  fenestra 
ovalis  would  be  too  great,  which  the  elasticity  of  the  chain 
and  its  articulations  prevent.  The  tympanum  can  only  exert 
a  limited  pressure  on  the  fenestra  ovalis,  and  when  it  is  at 
its  greatest  distance  from  it,  the  stapes  is  held  in  its  place,  in 
front  of  this  opening,  by  its  muscle.  This  is  the  theory  of 
Savart,  which  was  adopted  and  developed  by  M.  Longet. 

The  walls  of  the  tympanum  inclose  air,  which  propagates 
the  vibrations  from  the  tympanum,  and  transmits  them  by 
means  of  the  membrane  of  the  fenestra  rotunda  to  the  fluid 
of  the  labyrinth.  These  vibrations  lose  their  intensity  on 
becoming  aerial,  and  this  fact  has  led  to  the  idea  that  possibly 
they  may  differ  in  their  timbre  from  those  transmitted  by  the 
little  bones. 


HEARING.       THE    MIDDLE    EAR.  193 

However  this  may  be,  the  principal  use  of  the  air  in  the 
cavity  of  the  tympanum  is  not  to  transmit  the  vibrations  of 
that  membrane;  but  to  balance  the  pressure  of  the  atmosphere 
on  its  external  surface,  and  thus  to  render  it  completely  in- 
dependent between  two  equal  pressures.  This  is  effected  by 
means  of  the  Eustachian  tube,  which  conducts  the  air  into 
the  middle  ear.  The  temporary  obstruction  of  this  canal 
induces  buzzings  in  the  ear,  causing  temporary  deafness, 
which  is  intensified  by  its  entire  obliteration.  The  canal 
also  serves  as  an  outlet  for  mucus  and  other  fluids,  which 
may  be  secreted  in  the  cavity  of  the  tympanum. 

The  sonorous  waves  enter  the  vestibule  by  the  fenestra 
ovalis;  this  opening  is  closed  by  the  base  of  the  stapes,  and 
receives  the  vibrations  from  the  chain  of  little  bones.  The 
membrane  of  the  fenestra  rotunda  transmits  to  the  scala 
tympani  of  the  cochlea  the  aerial  vibrations  of  the  cavity  of 
the  tympanum.  This  membrane,  as  Scarpa  has  remarked,  is 
a  secondary  tympanum. 

On  reaching  the  labyrinth  the  vibrations  are  propagated  to 
the  fluid  which  bathes  it,  and  thus  reach  the  membranous 
labyrinth,  and  the  scala  vestibuli  of  the  cochlea,  where  finally 
they  encounter  the  extremities  of  the  ramifications  of  the 
auditory  nerve. 

Besides  the  sonorous  aerial  waves,  the  ear  perceives,  as 
has  already  been  stated,  those  which  have  been  caused  by 
an  impression  on  the  bones  of  the  skull.  Thus,  when  a 
sonorous  body  is  held  between  the  teeth,  or  against  the  walls 
of  the  cranium,  the  sound  is  perceived  by  the  auditory 
apparatus.  It  is  in  this  way  that,  in  spite  of  the  loss  of  the 
tympanum  and  the  small  bones  of  the  ear,  some  persons  can 
still  perceive  sounds  of  external  origin.  But  it  is  indispens- 
able that  the  membranes  of  the  fenestra  ovalis  and  fenestra 
rotunda,  which  close  the  openings  of  the  labyrinth  into  the 
cavity  of  the  tympanum,  should  still  remain  perfect,  and  that 
the  fluid  of  the  labyrinth  should  still  bathe  its  cavities.  But, 
as  may  be  easily  conceived,  hearing  under  these  circumstances 
is  very  limited,  since  it  can  only  take  place  when  the  sonor- 
ous body  is  in  contact  with  the  bones  of  the  head. 

The  functions  of  the  three  divisions  of  the  labyrinth  have 


194  THE    HUMAN    BODY. 

been  differently  stated  by  different  physiologists.  According 
to  Duges,  the  vestibule  concentrates  the  sound,  measures  the 
intensity,  and  consequently  judges  of  the  distance.  It  has 
been  supposed  that  the  semicircular  canals  either  give  the 
idea  of  the  direction  of  the  sonorous  waves,  and  of  the  posi- 
tion of  the  body  from  whence  they  emanate,  or  are  simply 
organs  for  increasing  the  sound.  De  Blainville  thinks  that 
the  function  of  the  cochlea  is  to  appreciate  very  acute  sounds, 
Duges  makes  it  the  musical  portion  of  the  auditory  organ, 
the  appreciator  of  notes,  and  the  special  apparatus  for  the 
perception  of  voices  and  articulate  sounds. 

Other  authors  have  thought  that  the  spiral  plate  (lamina 
spiralis),  which  narrows  regularly  from  the  base  to  the  summit 
of  the  cochlea,  corresponds  to  the  scale  of  notes,  from  the 
gravest  to  the  most  acute,  and  that  it  vibrates  in  unison 
with  each  one  of  them. 

According  to  Miiller  and  Longet,  the  object  of  the  cochlea 
is  to  furnish  a  solid  plate  upon  which  to  spread  the  nervous 
filaments,  in  contact  with  the  bony  walls  of  the  labyrinth  and 
of  the  head,  as  well  as  with  the  fluid  of  the  labyrinth;  thus 
being  able  to  transmit  to  these  filaments  the  vibrations  com- 
municated to  the  solid  or  fluid  portions  of  the  auditory 
apparatus.  And  also,  the  spiral  form  of  the  cochlea  gives  in 
the  least  possible  space  a  relatively  large  extent  of  surface 
for  the  expansion  of  the  nervous  filaments. 

This  diversity  of  opinion  is  easily  understood,  the  moment 
we  pass  from  natural  facts  to  physiological  speculations. 

The  auditory  nerve  is  distributed  to  every  portion  of  the 
labyrinth;  but  before  entering  it,  while  in  the  internal  auditory 
canal,  it  divides  into  two  branches,  the  smaller  one  running 
to  the  cochlea,  and  the  larger  to  the  vestibule  and  the  semi- 
circular canals.  If  we  admit  that  the  two  branches  are  homo- 
geneous, and  only  constitute  two  divisions  of  the  auditory 
nerve,  we  must  conclude  that  the  auditory  impression  is  per- 
ceived all  over  the  labyrinth,  just  as  the  visual  impression  is 
felt  on  every  portion  of  the  retina.  The  division  of  the 
nerve,  and  the  peculiar  disposition  of  the  ramifications  in 
each  of  the  labyrinthine  cavities,  seem  to  indicate  a  special 
function  for  each  of  these  cavities.  It  seems  natural  to  sup- 


HEARING.       THE    INTERNAL    EAR.  195 

pose  that  apparatus  so  different  in  form,  and  so  distinct 
in  the  different  parts  of  the  organ,  should  have  a  special 
object,  and  that  they  combine  their  functions  to  produce  the 
complex  sensation  of  hearing.  Miiller  has  demonstrated  that 
the  same  aerial  vibrations  act  with  much  more  intensity  on 
the  fluid  of  the  labyrinth,  after  having  traversed  the  chain  of 
small  bones  and  the  fenestra  ovalis,  than  they  do  after 
traversing  the  air  in  the  cavity  of  the  tympanum,  and  the 
membrane  of  the  fenestra  rotunda ;  he  thinks  that  the  waves 
of  the  same  sound  transmitted  through  the  two  fenestrse 
differ  not  only  in  intensity,  but  also  in  their  timbre  up  to  a 
certain  point,  since  those  reaching  the  fenestra  rotunda  are 
aerial  vibrations,  and  those  reaching  the  fenestra  ovalis,  by 
the  chain  of  small  bones,  are  in  the  state  of  vibrations  of 
solid  bodies.  But  the  cochlea  also  receives  sonorous  waves 
of  both  kinds  by  the  scala  tympani  and  the  scala  vestibuli; 
and  farther,  the  cavities  which  form  the  labyrinth  communi- 
cate with  them,  all  being  filled  with  a  common  fluid,  and 
all  united  by  their  walls ;  they  would  seem  therefore  to  be 
bound  together  up  to  a  certain  point  as  regards  auditory  im- 
pressions, and  nothing  demonstrates  that  vibrations  are  elec- 
tively  directed  in  their  movement  on  leaving  the  vestibule, 
either  toward  the  cochlea  or  the  semicircular  canals. 

It  must  be  admitted  notwithstanding,  that  authors  gener- 
ally agree  in  placing  the  principal,  and  indeed  only  seat  of 
auditory  impressions  in  the  cochlea,  and  this  is  the  doctrine 
now  professed  by  M.  Helmholtz,  to  whom  we  owe  our  know- 
ledge of  the  origin  and  mechanism  of  the  timbre  of  sounds. 
We  will  briefly  state  his  theory  of  hearing. 

We  have  already  seen  that  the  terminal  filaments  of  the 
acoustic  nerve  spread  themselves  regularly  side  by  side  over 
the  lamina  spiralis  of  the  cochlea,  like  the  cords  of  a  key- 
board; the  eminent  professor  of  Heidelberg  compares  these 
nervous  filaments  to  the  strings  of  a  piano,  and  explains  their 
functions  in  the  following  manner.  If  the  piano  be  opened, 
and  a  person  sings  loudly  above  the  strings  any  note  what- 
ever, the  sonorous  waves  cause  the  strings  which  respond 
to  the  harmonics  of  the  voice,  to  vibrate  also;  each  one  of 
these  strings  vibrates  exclusively  in  unison  with  one  har- 


196  THE    HUMAN    BODY. 

monic,  and  the  note  is  thus  decomposed  by  their  sympathetic 
vibration.  The  same  phenomenon  takes  place  in  the  in- 
ternal ear.  The  fibres  of  Corti  decompose  the  sounds,  each 
one  vibrating  in  unison  with  the  harmonic  with  which  it 
accords,  arid  these  vibrations  transmitted  collectively  to  the 
brain  by  the  acoustic  nerve  give  the  sensation  of  the  funda- 
mental note,  and  of  its  timbre.  But  here,  as  in  every  other 
instance,  the  living  organ  is  infinitely  superior  to  the  machine 
constructed  by  man.  The  fibres  of  Corti  number  upwards  of 
three  thousand,  and  this  gives  four  hundred  sensitive  cords 
to  each  octave,  of  which  the  interval  or  space  is  one  sixty- 
sixth  of  a  note.  It  is  easy  to  understand  from  this  how  a 
cultivated  ear  can  appreciate  the  slightest  difference  in 
sounds,  as  the  eye  perceives  the  least  difference  in  the 
degrees  of  light. 

This  theory  explains  one  of  the  most  mysterious  parts  of 
the  mechanism  of  audition,  it  shows  us  the  sonorous  waves 
exciting  the  Eolian  harp  of  the  acoustic  nerve,  just  as  direct 
observation  enables  us  to  see  the  luminous  image  painted  on 
the  retina.  Just  as  a  mirror  and  the  camera  obscura  repre- 
sent the  eye,  an  instrument  of  music  represents  the  ear;  and 
we  follow  the  sonorous  and  the  luminous  waves  to  the  point 
where  all  is  shrouded  in  mystery — to  sensation,  to  comprehend 
which  we  must  as  little  pretend,  as  to  penetrate  the  mystery 
of  life,  or  of  our  own  intelligence. 

But  the  ingenious  explanation  of  M.  Helmholtz  does  not 
at  first  seem  to  make  the  phenomena  of  hearing  as  accessible 
as  those  of  seeing  have  become  by  means  of  optical  instru- 
ments. The  convex  mirror,  and  the  productions  of  photo- 
graphy, show  us  magnificent  monuments  and  vast  landscapes 
reproduced  in  microscopic  proportion;  we  have  nothing  like 
this  for  the  ear,  and  we  are  involuntarily  led  to  contrast  the 
auditory  organ  and  its  fine  canals  with  the  grandeur  of 
sounds,  and  of  the  bodies  from  which  they  emanate.  Phy- 
sicists admit  that  the  sonorous  waves  cross  each  other  in  the 
air  in  nearly  the  same  manner  as  in  a  fluid,  without  modify- 
ing their  curves,  and  it  is  thus  that  the  distinctness  of  each 
particular  sound  is  perceived  in  an  accord  executed  by 
several  different  instruments;  but,  in  order  that  this  pheno- 


ACUTENESS   AND    DELICACY   OF    HEARING.  197 

menon  of  hearing  may  be  displayed,  the  sonorous  waves 
must  move  through  the  windings  of  the  labyrinth  with  the 
same  facility  that  they  traverse  space;  the  rush  of  meteors, 
and  the  immeasurable  voices  which  nature  has  given  to  the 
atmosphere,  to  the  ocean,  and  to  mountains,  must  be  trans- 
mitted to  our  ears  in  their  relative  proportions,  as  well  as 
the  sound  of  a  falling  dew-drop.  How  can  the  ear  in  its 
infinitesimal  proportions  perceive  with  equal  precision  the 
sound  of  the  gigantic  instruments  which  vibrate  under  the 
hand  of  nature,  and  the  feeblest  noise  which  traverses  the 
air? 

Let  us  remember  that  if  we  get  a  glimpse  of  the  details 
of  natural  phenomena,  and  of  those  movements  which  con- 
stitute life,  it  is  not  in  considering  them  as  a  whole,  but  in 
analyzing  them  as  far  as  our  limited  means  will  permit.  In 
the  vibrations  of  the  globe  of  air  which  surrounds  our  planet, 
as  in  the  undulations  of  the  ether  which  fills  the  immensity 
of  space,  it  is  always  by  molecules  which  are  intangible  for  us, 
put  in  motion  by  nature,  always  by  the  infinitely  little,  that 
she  acts  in  exciting  the  organs  of  sense,  and  she  has  modelled 
these  organs  in  a  proportion  which  enables  them  to  partake 
in  the  movement  which  she  impresses  upon  the  universe. 
She  can  paint  with  equal  facility  on  a  fraction  of  a  line  of 
space  on  the  retina,  the  grandest  landscape  or  the  nervelets 
of  a  rose-leaf;  the  celestial  vault  on  which  Sirius  is  but  a 
luminous  point,  or  the  sparkling  dust  of  a  butterfly's  wing : 
the  roar  of  the  tempest,  the  roll  of  thunder,  the  echo  of  an 
avalanche,  find  equal  place  in  the  labyrinth  whose  almost 
imperceptible  cavities  seem  destined  to  receive  only  the 
most  delicate  sounds. 

Acnteness  and  delicacy  of  hearing. — It  has  been  said  that 
hearing  is  the  most  perfect  of  the  senses  in  man.  Considered 
as  a  musical  instrument  the  ear  is  in  fact  a  most  admirable 
organ,  and  which  man  alone  possesses;  but  here,  as  in  the 
eye,  we  must  distinguish  between  the  apparatus  of  hearing 
and  what  pertains  to  the  domain  of  the  mind.  The  ear 
perceives  sounds,  but  the  mind  estimates  their  regularity, 
measures  their  intervals,  judges  them  melodious  or  the  re- 
verse, determines  their  discord  or  their  harmony.  If  the 


198  THE   HUMAN    BODY. 

painter  is  provided  with  a  faithful  mirror,  the  ear  is  for  the 
musician  a  still  more  infallible  guide;  not  that  it  surpasses  the 
eye  in  delicacy  of  mechanism,  but  that  the  mathematical  divi- 
sions of  sound,  and  of  their  intervals,  much  more  minute 
than  shades  of  colour,  do  not  admit  of  confusion.  The  eye 
perceives  a  great  number  of  tints  at  the  same  time,  which 
may  mingle  upon  the  retina  either  from  their  vicinity,  or  from 
the  rapid  displacement  of  objects,  as  we  see  when  the 
molecules  of  two  colours  are  mixed  together,  and  when  a 
disk  of  several  colours  turns  on  its  axis.  On  the  contrary, 
however  rapid  the  movement  in  a  piece  of  music,  each  note 
produces  a  distinct  sound,  and  when  several  reach  it  simulta- 
neously they  always  cause  isolated  impressions.  It  is  thus 
that  a  musician  in  the  midst  of  the  accords  of  a  large  or- 
chestra is  able  to  distinguish  a  false  note  and  the  instrument 
from  which  it  proceeds. 

The  acuteness  of  hearing  has  more  influence  upon  the 
delicacy  of  auditory  impressions,  than  extent  of  vision  has 
upon  visual  impressions;  acute  vision  is  not  necessary  to  the 
painter  in  judging  exactly  of  colours,  but  the  ear  of  the 
musician  must  have  an  exquisite  sensibility  in  order  that  he 
may  appreciate  the  truthfulness  of  notes  and  their  harmonic 
relations;  but  when  once  this  idea  is  acquired  it  is  ineffaceable, 
and  enables  him  to  create  master-pieces  which  his  ear  cannot 
hear.  Beethoven  became  deaf  at  forty,  and  composed  all 
those  immortal  works  which  for  himself  were  never  per- 
formed except  in  his  mind. 

It  is  not  rare  to  find  persons  who  distinguish  musical 
sounds  with  difficulty  and  confound  them  as  regards  the 
notes.  For  those  in  whom  this  Daltonism  of  the  ear  is  ex- 
treme, music  has  no  existence;  they  hear  only  a  succession 
of  sounds  more  or  less  intense,  without  harmonious  relation 
or  rhythmical  succession.  Between  this  condition  and  that 
delicacy  of  ear  which  marks  the  leader  of  an  orchestra  or  a 
good  tuner,  the  degrees  are  infinitely  varied,  and  absolute 
correctness  of  ear  is  as  rare,  at  least,  as  a  perfect  perception 
of  colour,  although  musical  impressions  seem  to  demand 
less  effort,  and  to  be  a  more  common  endowment  than  the 
ability  to  appreciate  painting. 


MUSICAL    EAR.       INTENSITY    OF   SOUNDS.  199 

It  is  said  that  a  false  note  disturbs  more  than  false  colour- 
ing, but  this  is  true  only  within  certain  limits.  A  mediocre 
amateur  listening  to  the  overture  of  "Der  Freischiitz"  at  the 
Conservatory  would  be  shocked,  no  doubt,  if  the  horn  should, 
by  one  of  those  accidents  which  it  is  impossible  always  to 
avoid,  be  out  of  tune;  but  the  same  amateur  after  having 
heard  this  same  piece  executed  by  a  second-rate  orchestra 
would  be  very  well  satisfied  with  the  concert,  and  would 
take  into  account  neither  the  false  notes  which  might  have 
escaped  nor  the  want  of  regard  to  time  or  expression,  and  if 
he  does  not  place  the  two  orchestras  on  the  same  level,  it 
will  be  from  personal  feelings.  Among  the  crowds  which 
visit  the  galleries  of  the  Louvre  every  year,  how  many  people 
prefer  a  common  and  inharmonious  picture  blazing  with 
colour  to  a  master-piece  of  Titian  ! 

A  person  who  sings  falsely  is  said  to  have  "no  ear,"  and 
often,  in  fact,  it  is  to  the  want  of  exactness  in  the  ear  that 
the  faults  in  the  voice  are  due.  In  this  case  the  evil  is*  be- 
yond remedy,  the  musician  who  has  an  incorrect  ear  can 
never  be  sure  of  producing  correct  sounds.  But  if  the  falsity 
of  the  note  is  due  solely  to  an  imperfection  in  the  vocal 
organ,  a  man  who  cannot  sing  correctly,  can  play  the  violin 
or  violincello  perfectly,  because  his  ear  judges  correctly  of 
the  sounds  which  he  produces  from  his  instrument. 

Intensity,  distance,  and  direction  of  sounds. — As  we  have 
seen,  authors  do  not  agree  upon  the  functions  of  the  different 
parts  of  the  auditory  apparatus  in  the  perception  of  the  in- 
tensity, the  distance,  and  the  direction  of  sound.  The  per- 
ception of  the  intensity  of  sound  seems  to  depend  more  on 
the  relative  perfection  of  the  whole  organ  than  on  any  one 
of  its  parts.  Vibrations  are  transmitted  to  every  part  of  the 
ear,  and  even  to  the  whole  body,  in  loud  noises  and  sounds. 
Thus  thunder,  the  report  of  cannon,  the  grave  notes  of  an 
organ  or  of  a  double-bass  viol,  cause  a  tremor  in  the  whole 
body;  but  it  is  by  the  vibratory  excitement  of  the  auditory 
nerve  that  we  judge  of  the  intensity  of  sounds,  as  the  optic 
nerve  enables  us  to  appreciate  that  of  light. 

In  regard  to  distance,  if  it  is  a  sound  with  which  we  are 
familiar,  that  of  the  human  voice,  for  example,  we  judge  of 


200  THE    HUMAN    BODY. 

it  by  the  greater  or  less  force  of  the  auditory  impression.  As 
for  noises  of  which  we  do  not  know  the  intensity  at  a  given 
distance,  as  thunder,  we  estimate  it  in  the  same  way,  but 
with  less  certainty  according  as  it  is  faint  or  loud. 

It  is  therefore  to  reasoning,  founded  on  the  sensation,  that 
we  owe  the  ability  to  judge  of  the  distance  as  well  as  the 
intensity  of  sounds,  and  it  is  the  same  as  to  their  direction. 
When  we  hear  a  sound  more  distinctly  with  one  ear  than 
with  the  other,  we  judge  that  it  comes  from  the  side  on 
which  the  impression  is  strongest,  and  the  ability  of  the 
organ  to  seize  slight  degrees  in  the  intensity  enables  us  to 
tell  in  what  position  of  the  head  the  sound  is  most  clearly 
perceived.  We  are  therefore  led  to  place  it  in  a  certain 
position  in  regard  to  the  direction,  and  by  this  means  we 
acquire  an  idea  of  it  within  certain  limits.  Hence,  if  the 
ears  are  both  in  the  same  situation  relative  to  the  sound,  as 
when  it  is  in  front  of  or  behind  us  for  example,  we  find  it 
impossible  to  distinguish  in  which  direction  it  is  without 
turning  the  head. 

This  uncertainty  which  we  always  feel  in  regard  to  the 
exact  distance  and  direction  of  sounds  enables  the  ventrilo- 
quist to  produce  what  are  wrongly  supposed  to  be  illusions 
of  hearing,  but  which  are  simply  errors  of  judgment  guided 
by  the  imagination.  The  hollow,  feeble  voice  of  the  ven- 
triloquist seems  to  come  from  a  great  distance,  from  above 
or  from  a  certain  depth  below  us,  the  sense  of  the  words,  the 
expression  of  the  voice,  the  varied  tones  and  mimicry  of  the 
juggler,  do  the  rest. 

Duration  of  auditory  impressions. — Savart  has  demonstrated 
that  the  duration  of  acoustic  impressions  is  about  the  tenth 
of  a  second.  Thus  when  the  vibrations  of  a  body  do  not 
exceed  nine  in  a  second,  the  ear  perceives  a  series  of  distinct 
impressions,  but  beyond  ten  or  twelve  the  sensation  becomes 
continuous. 

Sensations  of  internal  origin. — As  the  eye  may  be  the  seat 
of  luminous  impressions  produced  by  other  means  than  light, 
so  sounds  and  noises  may  be  heard,  without  the  ears  having 
been  excited  by  sonorous  waves.  Ringing  and  humming 
sensations  may  be  produced  in  or  imparted  to  them,  under 


PARALLEL  BETWEEN  THE  EAR  AND  EYE.       2OI 

abnormal  conditions  into  which  we  shall  not  inquire;  and 
of  which  the  mechanism  is  obscure  or  unknown.  A  pro- 
longed shock  to  the  auditory  nerve  by  a  loud  sound  or  noise 
will  cause  a  persistent  confused  sensation,  which  is  felt  by 
everyone  after  a  long  journey  by  railway,  or  after  being  near 
a  great  waterfall  or  in  a  mill  for  a  length  of  time. 

Parallel  between  the  ear  and  the  eye. — The  eye  and  the  ear 
present  many  analogies,  both  in  regard  to  their  functions 
and  their  anatomy.  The  pavilion  of  the  ear  has  been  com- 
pared to  the  eyelids,  the  auditory  canal  to  the  anterior 
chamber  of  the  eye,  the  tympanum  to  the  iris,  the  cavity  of 
the  tympanum  to  the  posterior  chamber,  the  small  bones  to 
the  crystalline,  and  the  liquor  Cotunnii  to  the  vitreous  body. 
These  organs  differ  in  their  nature,  like  the  exciting  agents 
which  pass  through  them.  Sound  and  light  both  originate 
in  vibrations,  but  transparency  is  the  essential  condition  of 
the  organ  through  which  light  passes,  while  sounds  are  pro- 
pagated through  all  bodies,  solid,  fluid,  or  gaseous. 

The  sense  of  light  enables  man  to  contemplate  the  admir- 
able spectacle  of  the  universe,  but  for  the  eye  nature  is 
mute ;  to  it  motion  alone  denotes  life ;  hearing  completes 
our  impressions,  everything  is  animated  by  it,  and  man  takes 
part  in  the  life  of  the  external  world,  and  shares  the  thoughts 
of  his  fellows.  The  perfection  of  these  two  senses  enables 
us  the  better  to  appreciate  the  connection  between  the 
functions,  and  the  unity  of  our  organs.  The  sight  speaks 
more  directly  to  the  intelligence,  it  enlarges  the  field  of 
thought,  it  gives  birth  to  precise  notions  of  light,  of  form, 
of  extent;  and  it  permits  the  communication  of  thought  by 
conventional  signs.  Hearing  is  a  necessary  condition  of 
articulate  language ;  without  it  man  lives  alone,  affection  and 
confidence  lose  their  most  precious  forms  of  expression,  and 
friendship  cannot  exist. 

Auditory  sensations  act  upon  the  nervous  system  with 
more  force  than  visual  sensations.  We  are  carried  away  by 
rhythm,  or  it  adapts  itself  to  our  ideas  and  our  passions; 
music  plunges  us  into  an  ideal  world,  and  holds  us  by  an  in- 
definable charm;  in  a  word,  if  sight  speaks  more  especially 
to  the  intellect,  hearing  addresses  itself  to  the  affections. 


2O2  THE    HUMAN    BODY. 

Sight  is  certainly  more  necessary  to  man  than  hearing,  but 
still  the  blind  are  generally  gay  and  communicative,  while 
the  deaf  seem  inclined  to  melancholy.  As  to  the  relative 
influence  of  these  two  senses  on  the  development  of  the 
intellect,  we  know  that  the  education  of  the  deaf  is  slow  but 
may  be  complete,  while  that  of  the  blind  is,  on  the  contrary, 
rather  rapid,  but  is  almost  always  very  limited;  many  ideas 
cannot  be  acquired  by  them,  and,  as  has  been  remarked  by 
M.  Longet,  their  minds  rarely  attain  maturity. 


CHAPTER  XIII. 


Sense  of  smell.  Olfactory  organs. — Nose;  nasal  fossa ;  turbinated  bones, 
pituitary  membrane. — Olfactory  nerve. — Odoriferous  principles;  their  de- 
velopment,  their  action  on  the  nervous  system. — Smell, — its  seat;  dura- 
tion of  olfactory  impressions. — Uses,  and  acuteness  of  smell. 


Olfactory  organs. — The  smelling  apparatus  is  situated  in 
the  middle  of  the  "face,  between  the  orbital  cavities  and  the 
palatine  arch.  Placed  thus  above  the  organ  of  taste,  which 
it  resembles  in  many  respects,  it  forms  the  entrance  to  the 
respiratory  passages,  and  controls  to  a  certain  extent  the 
purity  of  the  air  which  enters  them.  It  is  composed  of  the 
nose  and  the  nasal  fossae. 

The  nose. — Two  thin,  flattened  bones,  slightly  curved  in 
their  breadth,  form  the  superior  portion  of  the  nose.  They 
are  articulated  by  their  internal  border  in  the  median  line; 
at  their  external  border  they  are  united  to  the  ascending 
processes  of  the  upper  jaw,  and  they  are  attached  at  the  root 
of  the  nose  by  sutures  to  the  frontal  bone.  Their  inferior 
borders  are  attached  to  the  cartilages  which  complete  the 
nasal  walls.  The  arch  formed  by  the  nasal  bones  is  sup- 
ported by  a  bony  partition,  to  which  is  attached  a  cartila- 
ginous plate,  which  divides  the  nasal  cavity  into  two  symmet- 
rical halves,  and  separates  the  nostrils.  A  delicate  skin 
envelops  the  nose  and  covers  its  little  muscles,  which  are 
more  important  from  a  physiognomical  point  of  view  than 
from  their  organic  functions. 

Nasal  fossa. — This  is  the  name  applied  to  two  irregular 
cavities  which  are  continuous  with  the  nasal  cavities;  they 
rest  against  each  other  on  the  median  line,  and  are  bounded 
below  by  the  palatine  arch,  and  above  by  the  cribriform 


204  THE    HUMAN    BODY. 

plate  (cribrum,  a  sieve,  being  perforated  with  numerous  holes) 
of  the  ethmoid  bone.  They  open  posteriorly  just  above  the 
throat.  A  partition  formed  by  the  perpendicular  plate  of  the 
ethmoid,  the  vomer  (a  ploughshare),  and  a  cartilage  separates 
the  nasal  fossae  on  the  median  line ;  the  prolongation  of  this 
cartilage  separates  the  nasal  cavity  into  two  parts,  as  we  have 
already  seen.  On  the  external  walls  of  the  nasal  fossae  there 
are  bony  folds,  which  are  called  upper,  middle,  and  lower 
spongy  bones,  and  are  separated  from  each  other  by  corre- 
sponding passages.  The  nasal  fossae  communicate  with 
numerous  sinuses  in  the  substance  of  the  bones  of  the  face 
and  skull. 

The  whole  internal  surface  of  the  olfactory  apparatus  is 
lined  with  a  mucous  membrane  called  the  pituitary  mem- 
brane, this  is  the  immediate  organ  of  smell.  This  membrane 
dips  into  the  numerous  inequalities  of  the  spongy  bones  and 
the  passages,  thus  presenting  a  larger  surface  to  olfactory 
impressions.  The  olfactory  nerve  is  ramified  in  the  pituitary 
membrane.  It  penetrates  the  nasal  fossae  through  the  cribri- 
form plate  of  the  ethmoid,  but  is  distributed  over  the  upper 
portion  only.  In  the  lower  portion  of  the  fossae  the  pituitary 
membrane  receives  only  nervous  filaments  from  the  fifth 
pair,  a  circumstance  to  be  noted  in  reference  to  the  mechan- 
ism and  seat  of  smell. 

Odours. — The  philosopher  calculates  the  velocity  and  in- 
tensity of  light,  he  can  analyze  it,  he  knows  from  what  sub- 
stance a  given  colour  emanates,  and  if  this  substance  exists 
in  the  star,  the  rays  of  which  he  is  observing;  he  demon- 
strates in  the  vibrations  of  bodies  the  origin  of  the  sonorous 
waves,  and  sees  in  light  as  in  sound,  not  particles  of  matter 
traversing  space,  but  a  movement  excited  in  the  surrounding 
media.  Some  learned  men  have  thought  that  odours  also 
result  from  a  vibratory  movement  transmitted  to  the  ambient 
air  by  the  molecules  of  odoriferous  substances,  but  Fourcroy 
demonstrated  the  origin  of  odoriferous  emanations  in  the 
volatility  of  the  immediate  materials  of  vegetables;  and 
odours  are  now  generally  considered  as  bodies  existing  by 
themselves,  and  not  as  a  purely  physical  result  comparable 
to  sonorous  or  luminous  waves;  they  are  extremely  minute 


MINUTENESS    OF    ODORIFEROUS    PARTICLES.  205 

material  particles,  volatilized  in  the  atmosphere.  But  here 
matter  seems  to  become  intangible.  The  chemist  can  ex- 
tract from  a  body  the  essential  oil  which  gives  it  its  odour, 
but  he  cannot  separate  the  odoriferous  principle  from  the  oil 
itself,  and  he  can  only  recognize  its  presence  by  the  special 
impression  received  by  the  olfactory  nerve. 

Nothing  gives  us  a  more  exact  idea  of  the  divisibility  of 
matter  than  the  diffusion  of  odours.  Three-quarters  of  a  grain 
of  musk  placed  in  a  room  cause  a  very  powerful  smell  for  a 
considerable  length  of  time  without  any  sensible  diminution 
in  weight,  and  the  box  in  which  musk  has  been  placed 
retains  the  perfume  for  an  almost  indefinite  period.  Haller 
relates  that  some  papers  which  had  been  perfumed  by  a 
grain  of  ambergris,  were  still  very  odoriferous  after  a  lapse 
of  forty  years. 

Odours  are  transported  by  the  air  to  a  considerable  dis- 
tance. A  dog  recognizes  his  master's  approach  by  smell 
even  when  he  is  far  away;  and  we  are  assured  by  navigators 
that  the  winds  bring  the  delicious  odours  of  the  balmy  forests 
of  Ceylon  to  a  distance  of  ten  leagues  from  the  coast. 

Simple  experiments  prove  that  odoriferous  bodies  emit  a 
stream  of  particles  so  small  as  to  seem  to  be  immaterial. 
When  a  morsel  of  camphor  or  a  small  body  saturated  with 
ether,  or  minute  portions  of  benzoic  acid,  are  thrown  upon 
water,  they  are  animated  by  a  peculiar  movement,  which  is 
due  to  the  propulsion  produced  by  the  invisible  vapour 
which  emanates  from  these  substances. 

Heat,  light,  and  other  influences  modify  the  production  of 
odours,  and  their  transmission  in  space.  Certain  plants  are 
odoriferous  only  at  night,  and  it  is  especially  in  the  morning 
and  evening,  when  the  dew  is  scanty,  that  flower-gardens 
perfume  the  atmosphere.  Rain  destroys  the  perfume  of 
flowers,  probably  by  its  mechanical  action,  and  by  lowering 
their  temperature.  It  is  remarkable  also  that  animal  or 
vegetable  odours  are  feebler,  as  the  countries  are  colder  in 
which  the  plants  or  animals  live  from  which  they  emanate. 
Hence  perfumes  come  principally  from  tropical  countries. 

It  has  been  stated  that  substances  absorb  and  retain  odours 
according  to  their  colour,  Thus,  the  experiments  of  Stark 


206  THE    HUMAN    BODY. 

tend  to  prove  that  black  garments  are  more  quickly  impreg- 
nated with  an  odour,  and  retain  it  longer,  than  light-coloured 
garments.  On  the  other  hand,  A.  Dumeril  assures  us  he  has 
ascertained  that  white  stuffs  absorb  odours  as  quickly  as 
others,  but  that  the  odoriferous  particles  are  sooner  evapor- 
ated from  them.  There  must  consequently  be  in  this  respect 
a  difference  in  odours  like  that  in  luminous  rays,  but  the  first 
of  these  phenomena  has  not  been  at  all  so  clearly  demon- 
strated as  the  latter. 

Under  the  influence  of  a  shock,  or  from  friction,  certain 
vegetable  and  mineral  bodies  emit  odours  more  or  less  power- 
ful. Such  are  several  varieties  of  wood,  especially  lilac  and 
Saint  Lucy,  the  leaves  of  mint,  lemon  verbena,  and  southern- 
wood, and  certain  calcareous  or  silicious  rocks.  Other  plants, 
on  the  contrary,  lose  their  aroma  on  being  bruised,  like  the 
mignonette,  the  violet,  &c.  The  contact  of  water,  or  of 
vapour,  also  develops  odours  in  argillaceous  rocks  and 
several  vegetable  substances. 

Odours  have  a  very  marked  effect  on  the  nervous  system; 
but  some  persons  are  far  more  impressible  in  this  respect 
than  others.  There  is  no  doubt  that  certain  odours  may 
cause  grave  disturbance  in  the  nervous  system;  but  the  ima- 
gination sometimes  plays  a  prominent  part  in  the  discomfort 
produced  by  a  bouquet  of  roses  or  violets;  the  sight  of  artifi- 
cial flowers  is  sometimes  sufficient  to  excite  persons  painfully 
who  believe  them  to  be  natural.  People  often  ascribe  to 
this  influence  of  odours  on  the  brain,  what  is  really  due  to  the 
effects  of  carbonic  acid  gas,  or  of  poisonous  emanations  ab- 
sorbed by  the  lungs;  and  how  many  persons  there  are  who 
do  not  believe  the  open  combustion  of  charcoal  is  innocuous, 
because  it  does  not  emit  so  much  smell  as  coal. 

But  even  after  making  due  allowance  for  the  effects  of  the 
imagination,  it  is  certain  that  odours  act  as  an  excitant  on 
the  brain,  which  may  be  dangerous  when  long  continued. 
They  are  especially  dreaded  by  the  Roman  women.  It  is 
well  known  that  in  ancient  times  the  women  of  Rome  in- 
dulged in  a  most  immoderate  use  of  baths  and  perfumes;  but 
those  of  our  times  have  nothing  in  common  with  them  in  this 
respect;  and  the  words  of  a  lady  are  quoted,  who  said  on 


SMELL.  207 

admiring  an  artificial  rose,  "It  is  all  the  more  beautiful  that 
it  has  no  smell." 

We  are  warned  by  the  proverb  not  to  discuss  colours  or 
tastes,  and  we  may  add  odours  also.  Men  and  nations 
differ  singularly  in  this  respect.  The  Laplander  and  the 
Esquimaux  find  the  smell  of  fish-oil  delicious.  Wrangel  says 
his  compatriots,  the  Russians,  are  very  fond  of  the  odour  of 
pickled  cabbage,  which  forms  an  important  part  of  their  food; 
and  assafcetida  is.  it  is  said,  used  as  a  condiment  in  Persia, 
and,  in  spite  of  its  name,  there  are  persons  who  do  not  find 
its  odour  disagreeable  any  more  than  that  of  valerian. 

Smell. — The  air  which  enters  the  organ  of  smell  deposits 
on  the  surface  of  the  pituitary  membrane  the  odoriferous 
principles  with  which  it  is  charged,  it  becomes  impregnated 
with  them,  arid  it  is  in  its  tissues  that  these  principles  come 
in  contact  with  the  terminal  fibres  of  the  olfactory  nerve. 
We  have  already  stated  that  this  nerve  is  only  distributed 
over  the  upper  portion  of  the  nasal  fossae;  in  order  to  produce 
the  sensation  of  odours,  therefore,  the  air  inspired  must  reach 
not  only  the  inferior  but  also  the  superior  parts  of  these 
cavities.  The  nose  is  contracted  at  the  root  like  a  funnel, 
and  tends  to  guide  the  odoriferous  effluvia  towards  the  point 
where  the  impression  is  to  be  perceived;  and  the  stronger 
the  inspiration  the  higher  up  the  column  of  air  is  carried,  and 
the  more  it  excites  the  filaments  of  the  special  nerve.  Some 
physiologists  have  thought,  with  Magendie,  that  the  nerves  of 
the  fifth  pair,  which  ramify  over  the  lower  portion  of  the 
pituitary  membrane,  were  designed  to  serve  the  purpose  of 
smell;  it  seems  to  be  clearly  demonstrated  that  the  sensa- 
tions caused  by  acid  or  ammoniacal  vapours  are  not  olfactory, 
but  simply  painful. 

The  pituitary  membrane  in  its  normal  condition  is  con- 
stantly humid,  and  the  secretion  with  which  it  is  bathed  is 
one  of  the  indispensable  conditions  of  the  function  of  smell; 
and,  therefore,  we  remark  at  the  commencement  of  a  cold  in 
the  head,  when  this  membrane  becomes  dry,  that  the  sense 
of  smell  is  more  or  less  impaired.  The  nose,  by  shielding 
the  membrane  from  the  immediate  contact  of  the  air,  pre- 
serves its  functions,  and  the  loss  of  this  organ  diminishes, 


208  THE    HUMAN    BODY. 

or  even  completely  destroys,  the  sense  of  smell.  Smelling 
is  ordinarily  involuntary,  but  it  may  be  rendered  more 
active  by  the  exertion  of  the  will.  The  inspirations  are 
then  stronger  and  more  frequent,  in  order  that  the  odour 
which  we  wish  to  perceive  or  enjoy  may  be  carried  in  greater 
quantity  toward  the  nasal  arch.  But  if,  on  the  contrary,  we 
wish  to  avoid  a  disagreeable  odour,  a  sudden  expiration  takes 
place  from  the  nose,  and  we  breathe  instinctively  through 
the  mouth,  and  the  soft  palate  closes  the  olfactory  cavities 
behind.  It  is  in  this  way  that  we  are  able  to  diminish  the 
disagreeable  impression  arising  from  the  odour  in  drinking 
sulphureous  waters. 

Whether  odours  reach  the  seat  of  smell  by  the  nose,  or 
through  the  posterior  opening  of  the  nasal  fossae,  the  result 
is  the  same;  it  is  by  this  means  that  we  perceive  the  aroma 
of  the  food  when  eating  with  the  mouth  shut;  but  under 
these  latter  conditions  the  persistence  of  the  impressions 
very  soon  blunts  the  sensibility.  A  man  fasting  immediately 
perceives  it,  if  a  man  with  whom  he  is  speaking  has  taken 
the  smallest  quantity  of  alcohol,  even  though  it  was  only  a 
glass  of  red  wine;  after  eating  we  distinguish  much  less  easily 
in  others  the  odour  of  the  aliments  of  which  we  ourselves 
have  partaken,  and  the  odoriferous  principles  of  which  have 
already  saturated  the  olfactory  membrane. 

The  sinuses  of  the  bones  of  the  skull  and  of  the  face, 
which  are  in  communication  with  the  nasal  fossae,  take  no  part 
in  the  perception  of  odours.  It  has  been  thought  that  they 
may  contribute  by  their  secretions  to  moisten  the  pituitary 
membrane,  or  serve  as  receptacles  for  the  air,  which  is  after- 
ward carried  from  their  cavities  to  the  organ  of  smell. 

Duration  of  olfactory  impressions. — When  we  have  inspired 
a  strong  and  penetrating  odour,  the  sensation  is  prolonged 
for  a  certain  time,  sometimes  for  several  hours.  It  is  pro- 
bable that  in  this  case  the  impression  is  not  single,  but  is  in- 
cessantly renewed  by  the  odoriferous  particles  with  which 
the  mucus  of  the  pituitary  membrane  is  impregnated,  or 
which  is  confined  in  the  air  in  the  sinuses.  Sometimes  also 
the  odour  has  penetrated  the  garments,  or  is  attached  to  the 
skin  or  the  hair,  and  from  thence  continues  its  impressions. 


ACUTENESS    OF    SMELL.  209 

% 

Any  vigorous  exercise,  or  eating,  by  exciting  the  secretions, 
generally  causes  the  sensation  to  disappear,  the  persistence 
of  which  might  be  exceedingly  inconvenient. 

Gerdy  makes  the  sense  of  smell  the  counsellor  of  the 
stomach.  When  the  appetite  is  excited  the  smell  of  food  is 
agreeable;  but  it  is  repugnant,  on  the  contrary,  when  hunger 
is  appeased,  and  the  sense  of  smell  warns  us  to  take  no  more 
food.  We  may  say,  with  reason  perhaps,  that  this  sense 
completes  that  of  taste,  by  enabling  us  to  appreciate  the 
aroma,  without  which  food  and  drink  would  cause  only  a 
gross  sensation,  or  one  at  least  entirely  devoid  of  all  delicacy. 
When  the  sense  of  smell  is  lost,  or  even  enfeebled,  the  taste, 
perceiving  flavours  only,  seems  almost  extinguished,  existing  - 
alone. 

The  sense  of  smell  is  very  unequally  developed  in  indivi- 
duals, but  it  is  said  to  be  of  extreme  delicacy  in  some  races 
of  men,  and  especially  among  savages.  The  stories  recounted 
of  individuals  following  game  by  tracking,  and  of  negroes 
who  could  distinguish  by  smell  the  tracks  of  a  negro  from 
those  of  a  white  man,  seem  to  indicate  a  faculty  quite  as 
nearly  related  to  the  sense  of  sight  as  to  the  one  under  con- 
sideration; and  it  must  be  admitted  also  that  individual  ex- 
perience and  careful  attention  to  particular  circumstances 
produce  the  same  results  when  applied  to  the  sense  of  smell, 
as  to  sight  or  to  hearing. 


CHAPTER   XIV. 


Sense  of  taste. — Organ  of  taste. — Special  nerves  of  the  organ. — Flavours. 
—  taste. 


Organ  of  taste. — In  describing  the  mouth  as  a  part  of  the 
digestive  apparatus,  the  functions  of  its  several  parts  were 
explained,  as  well  as  of  the  organs  which  surround  or  fill  its 
cavity.  It  is  only  requisite  here  to  repeat  that  the  tongue 
receives  three  nerves,  of  which  one,  the  great  hypoglossal, 
gives  it  motion;  and  the  two  others,  the  lingual  and  the 
glosso-pharyngeal,  give  it  gustatory  sensibility.  The  tongue 
participates  by  its  movements  in  the  digestive  functions,  and 
in  the  articulation  of  sounds;  but  it  has  besides  a  special 
sensibility — it  is  the  principal  organ  of  taste. 

Flavours,  taste. — The  cause  and  intimate  nature  of  tastes 
are  no  better  understood  than  those  of  odours.  It  is  by 
volatilization  that  the  intangible  particles  of  the  odoriferous 
principles  reach  us;  it  is  by  a  solution  more  or  less  complete 
that  substances  impart  their  flavour,  that  inherent  property 
which  taste  alone  reveals  to  us.  We  recognize  in  this  way 
their  acidity  or  saltness,  whether  they  are  sweet  or  bitter,  &c.; 
but  nothing  in  the  nature  of  bodies,  in  their  texture,  or  in 
their  constituent  elements,  has  ever  yet  explained  their 
sapidity.  Flavours  elude  analysis  and  defy  classification, 
even  that  which  divides  them  into  agreeable  and  disagreeable, 
for  the  taste  of  individuals  and  of  nations  singularly  differs  in 
this  respect.  The  Laplander  and  the  Esquimaux  drink  great 
quantities  of  train-oil,  which  for  them  is  a  greatly  esteemed 
article  of  food,  and  is  most  admirably  adapted  to  the  exigen- 
cies of  a  Polar  climate;  the  Abyssinians  eat  raw  flesh,  and 
find  its  flavour  excellent,  while  the  inhabitant  of  the  West 


FLAVOURS.  211 

partakes  of  it  with  the  greatest  repugnance,  and  only  as  a 
medicine.  Oysters,  which  are  so  generally  esteemed  in  our 
country,  are  to  some  persons  disagreeable  and  nauseous; 
and  truffles,  the  delight  of  the  gourmand,  are  rejected  by  the 
uninitiated  on  account  of  their  flavour  and  their  perfume.  It 
is  the  same  with  almost  all  alimentary  substances ;  they  are 
eagerly  sought  after  by  some,  and  despised  or  abhorred  by 
others.  Let  us  remember  the  proverb,  and  not  dispute  in 
regard  to  tastes;  each  is  suited  to  its  own  country,  and  goodly 
numbers  acclimatize  themselves,  to  the  great  advantage  of 
peoples,  among  whom  at  first  they  seem  exceedingly  strange. 
Man  should  control  his  taste,  and  habituate  it  to  all  whole- 
some aliment;  this  neither  excludes  choice,  nor  blunts  the 
delicacy  of  the  sense;  and  while  we  resist  its  seductions,  we 
should  give  timely  heed  to  its  instincts  and  its  counsels,  for 
they  are  often  invaluable. 

Among  the  substances  which  we  taste,  there  are  few  which 
address  themselves  solely  to  that  sense,  and  not  at  the  same 
time  to  the  sense  of  smell.  This  mingling  together  in  the 
same  substance  of  flavours  and  odours,  and  the  simultaneous 
action  of  the  senses  which  perceive  them,  has  induced  some 
authors  to  consider  them  as  forming  but  one.  They  are, 
notwithstanding,  quite  distinct  in  their  seat  and  in  their 
function;  the  mixed  sensation  resulting  from  the  union  of 
their  impressions  differs  entirely  from  that  which  they  cause 
singly;  we  may  say  that  the  sense  of  smell  is  the  necessary 
complement  of  taste,  for  the  latter  is  reduced  to  very  trifling 
importance  when  it  acts  alone. 

However  much  flavours  may  vary,  they  are  all  referable  to 
a  very  few  types,  to  the  mixtures  and  shades  of  which  we 
are  quite  indifferent  when  they  do  not  offend  us.  The  taste 
solely  judges  whether  a  substance  is  salt  or  sweet,  acid  or 
astringent,  and  so  forth;  but  when  our  food  does  not  awaken 
any  other  sensations,  we  are  tempted,  in  spite  of  its  flavour,  to 
pronounce  it  insipid;  vanilla  cream  and  coffee  cream,  or  ices 
with  rum  or  with  maraschino,  do  not  differ  in  taste  when  the 
nostrils  are  closed.  If,  instead  of  olive-oil  and  wine-vinegar, 
bleached  oil  and  acetic  acid  diluted  with  water  be  used  to 
,  season  a  salad,  we  shall  have  the  sensation  of  taste  without 


212  THE    HUMAN    BODY. 

that  of  smell.  We  must  not  then  confound  with  natural 
taste  that  which  smell  adds  to  it,  and  it  is  to  supply  the  lack 
in  this  respect  of  what  is  wanting  in  our  food  and  in  our 
blunted  senses  that  we  make  use  of  condiments. 

We  must  also  distinguish  the  bodies  the  action  of  which 
is  confined  to  the  sense  of  touch  exercised  by  the  tongue, 
and  many  impressions  reputed  to  be  those  of  taste  ought 
rather  to  be  considered  as  purely  tactile,  such  as  astringency, 
tartness,  the  irritating  or  caustic  action  of  certain  sub- 
stances, &c. 

On  this  principle  M.  Chevreul  has  divided  substances  into 
four  classes  according  to  the  impression  which  they  produce 
in  the  mouth:  ist,  bodies  acting  on  the  sense  of  touch  in  the 
tongue,  such  as  rock-crystal,  ice,  and  so  forth;  2d,  bodies 
acting  on  the  sense  of  touch  and  of  smell,  such  as  aromatic 
metals,  tin  and  copper  for  example;  3d,  bodies  acting  upon 
feeling  and  taste,  as  sugar-candy,  common  salt,  &c. ;  4th, 
bodies  acting  on  the  touch,  taste,  and  smell,  as  mint-lozenges, 
chocolate,  or  volatile  oils. 

All  alimentary  substances  figure  necessarily  in  the  latter 
class. 

Authors  do  not  agree  upon  the  seat  of  taste;  several  be- 
lieve it  extends  over  nearly  the  whole  surface  of  the  tongue, 
to  the  pillars  of  the  fauces,  and  to  the  upper  surface  of  the 
soft  palate,  to  the  tonsils,  and  to  the  pharynx.  It  is  now 
generally  believed  to  be  located  at  the  tip,  at  the  base,  and 
on  the  edges  of  the  tongue,  and  at  a  certain  limited  space 
on  the  anterior  surface  of  the  soft  palate.  According  to  M. 
Longet,  the  back  of  the  tongue  and  the  pillars  of  the  fauces 
are  not  entirely  destitute  of  gustatory  sensibility. 

Savoury  substances  do  not  produce  the  same  impression 
upon  all  parts  of  the  tongue,  many  salts  on  the  tip  of  the 
tongue  have  an  acid,  salt,  sharp,  or  styptic,  at  the  base  a 
bitter  or  metallic  taste;  others,  on  the  contrary,  have  the 
same  flavour  on  every  part.  In  general,  acidity  is  best  per- 
ceived at  the  tip,  and  on  the  edges  of  the  tongue,  saline  or 
metallic  flavours  are  developed  at  the  posterior  portion. 

In  order  to  perceive  the  flavour,  the  savoury  molecules 
must  be  bathed  in  saliva,  and  partially  dissolved,  so  as  to  be 


SEAT    OF    TASTE.  213 

placed  in  more  immediate  contact  with  the  surface  of  the 
tongue.  .  To  further  insure  this  contact,  the  tongue  applies 
itself  to  the  palatine  arch,  and  presses  the  food  against  its 
surface.  It  is  then  that  the  gustatory  impression  is  produced 
in  its  full  force,  and  from  this  it  has  been  inferred  that  the 
palate  is  the  principal  seat  of  taste.  The  action  of  the 
palate,  however,  is  purely  mechanical,  and  is  limited,  as  we 
have  stated,  to  securing  immediate  contact  between  the 
savoury  bodies  and  the  tongue.  This  is  demonstrated  by 
covering  the  palatine  arch  with  a  thin  pellicle  which  is  itself 
insipid  and  impermeable;  the  taste  is  just  as  acute  under 
-  these  conditions,  but  if  the  tongue  is  covered  with  this  same 
pellicle,  and  the  palate  uncovered,  no  taste  is  perceived. 
The  cheeks  and  lips  also  contribute  to  taste  by  carrying  the 
particles  of  food  which  may  have  fallen  outside  the  dental 
arch  during  mastication  back  to  the  tongue.  Taste  acts  not 
less  delicately  in  deglutition,  when  the  contents  of  the  mouth 
descend  between  the  base  of  the  tongue  and  the  soft  palate 
on  its  way  through  the  throat.  Food  and  drink  must  re- 
main for  a  certain  time  in  the  mouth  in  order  that  their  full 
flavour  may  be  perceived ;  thus  the  gourmand  takes  care  to 
retain  them,  and  exhaust,  as  it  were,  their  aromas,  before  send- 
ing them  to  the  stomach.  For  this  reason,  also,  wine-tasters 
hold  the  wine  in  their  mouth  when  they  wish  to  judge  of  its 
quality,  but  they  avoid  swallowing  this  mouthful  of  wine 
after  it  is  thus  robbed  of  its  bouquet;  they  reject  it  after 
thoroughly  moistening  the  surface  of  the  tongue,  and  they 
can  then  decide  as  to  the  vineyard  and  the  year  of  the 
vintage.  If  they  drank  the  wine  which  they  taste,  the  smell, 
which  here  plays  the  principal  part,  would  very  soon  become 
dulled. 

The  papillae  of  the  tongue,  it  is  generally  considered,  are 
endowed  with  gustatory  sensibility,  and  this  sensibility  is 
principally  attributed  to  the  fungiform  papillae.  According 
to  M.  Longet  they  are  rather  tactile  organs,  and  the  learned 
physiologist  supports  his  opinion  by  the  fact  that,  on  the 
point  of  the  tongue  the  taste  is  no  less  perfect  where  the 
parts  are  destitute  of  papillae,  while  the  feeling  there  is  much 
less  delicate  than  on  the  papillae  themselves. 


214  THE   HUMAN    BODY. 

The  impressions  of  taste  are  quite  persistent  according  to 
some  authors,  but  this  persistence  is  due  to  the  presence  of 
savoury  particles  on  the  tongue,  and  is  more  correctly  the 
constant  renewal  of  the  impression.  Experience  shows  how 
difficult  it  is  to  get  rid  of  certain  flavours,  and  it  is  easy  to 
understand  that  when  dissolved,  and  retained  by  the  saliva 
in  what  may  be  called  the  papillary  fleece  of  the  tongue,  the 
particles  remain,  and  furnish  for  a  considerable  time  the 
materials  for  the  sensation.  It  is  a  mechanism  analogous  to 
that  which  produces  the  persistent  smell  of  creosote  and 
dextrine  from  the  hands  several  hours  after  contact  with  the 
disgusting  perfume. 

Taste  is  but  slightly  developed  in  infancy,  and,  although 
it  acquires  some  delicacy  in  youth,  it  is  especially  in  mature 
age  that  it  reaches  its  perfection.  Far  from  growing  feeble 
with  the  lapse  of  years,  it  retains  all  its  acuteness,  and  con- 
soles the  aged  for  the  irreparable  injuries  of  time.  It  is  per- 
fected by  exercise,  and  attains  in  some  individuals  remarkable 
delicacy,  as  in  professional  tasters,  for  example;  but  the  pro- 
longed use  of  highly  seasoned  food,  the  abuse  of  alcoholic 
liquors,  and  above  all  of  tobacco,  enfeebles  and  blunts  it  in 
what  may  be  termed  its  olfactory  portion. 

The  question  has  been  raised  whether  taste  is  developed 
by  civilization.  This  is  admitted  by  several  physiologists, 
but  perhaps  it  would  be  necessary  to  establish  a  distinction 
between  the  natural  sensibility  of  the  organ  and  its  aptitude 
in  judging  of  a  great  number  of  flavours.  In  this  last  respect 
there  is  no  doubt  of  the  superiority  of  civilized  nations,  but 
there  is  great  difference  between  them  notwithstanding,  and 
if  we  were  to  measure  the  civilization  of  nations  by  the  deli- 
cacy of  their  taste,  we  might  arrive  at  very  flattering  con- 
clusions for  some,  it  is  true,  but  at  very  painful  ones  for 
many  others.  We  will  content  ourselves  with  saying  that, 
in  Europe,  the  taste  is  generally  more  developed  in  the  south 
than  in  the  north.  In  conclusion,  it  furnishes  very  little 
material  to  the  intellect.  Its  scientific  use  is  limited  to  in- 
dicating to  the  chemist  the  sapidity  and  species  of  flavour  of 
substances. 

Its  functions,  in  relation  to  nutrition,  dispose  to  gaiety  and 


POSITION    OF   TASTE    AMONG   THE    SENSES.  215 

good  humour,  and  nothing  except  labour  produces  a  more 
powerful  diversion  for  the  mind  of  a  person  a  prey  to  chagrin 
or  melancholy.  Stationed  at  the  entrance  to  the  digestive 
passages,  it  guides  us  in  the  choice  of  food,  and  controls  its 
nature  and  quality;  it  warns  us  against  repletion  by  its  indif- 
ference to  the  flavours  the  most  appreciated  at  the  beginning 
of  the  repast,  and  compensates  by  agreeable  sensations  for 
hunger — the  hard  necessity  of  our  organization. 

Taste  is  therefore  a  useful  servant,  but  on  the  whole  we 
see  that  of  all  our  senses,  it  is  not  the  farthest  removed  from 
matter,  and  what  is  worse  still,  it  has  much  to  be  pardoned 
for.  The  stomach  reproaches  it  with  not  being  so  virtuous 
as  physiologists  seem  to  believe,  and  accuses  it  of  being 
dangerously  seductive,  and  the  worst  enemy  of  those  who 
should  regulate  their  diet;  and  though  it  sometimes  gives 
timely  warning  by  disgust,  it  is  often  in  the  wrong  in  reject- 
ing wholesome  food  under  the  pretext  that  it  is  new  or  that 
its  prejudices  condemn  it.  The  taste  retorts  by  throwing  the 
blame  on  those  who  have  taught  it  to  be  fastidious;  it  pro- 
fesses, and  with  truth,  to  be  docile  to  training,  and  that  the 
prejudices  come  from  the  master  of  the  house;  and  it  adds 
that,  though  perfectly  competent  to  judge  of  the  merits  of  a 
cook,  it  is  very  little  acquainted  with  questions  of  hygiene, 
and  that  the  enemy  of  the  stomach  is  gluttony  and  not 
taste. 

Some  persons  affect  a  contempt  for  this  sense,  explicable, 
no  doubt  to  a  certain  extent,  but  which  tempts  us  to  be- 
lieve that  they  speak  of  it  only  from  hearsay.  "The  mind 
should  take  precedence  of  the  body,"  as  Belisus  emphatically 
declares;  but  the  good  Chrysalus,  was  he  wrong  in  saying, 
"Yes!  my  body  is  myself,  and  I  will  take  care  of  it?"  May 
we  not  remember  in  proper  time  and  place  that  "man  lives 
on  good  soup,  and  not  on  fine  words :"  besides,  one  does  no 
harm  to  the  other,  and  to  want  even  the  most  modest  sense 
is  to  be  imperfect  after  all.  Thenard,  speaking  of  cooking 
before  a  crowded  audience  at  the  Sorbonne,  called  it  "  that 
important  part  of  chemistry." 

We  may  think  what  we  please  of  the  taste,  but  it  has 
always  in  all  ages  been  the  endowment  of  men  of  genius. 


2l6  THE    HUMAN    BODY. 

In  reading  Brillat-Savarin,  we  feel  disposed  to  believe  that 
the  mind  and  the  gastronomic  senses  are  inseparable.  But 
these  are  delicate  questions;  and  as  we  would  not  toss  an 
apple  of  discord  between  nations,  neither  shall  we  between 
individuals,  but  rather  prudently  refer  the  reader  to  the 
Physiology  of  Taste. 


CHAPTER  XV. 


Sense  of  touch  — Difference  between  touch  and  feeling.  —  Tactile  sensibility 
and  general  sensibility1' — Organ  of  touch.  Sensation  of  contact ;  dif- 
ference in  the  sensibility  of  different  regions  of  the  body  ;  simple  contact, 
shock,  vibration. — Sensation  of  pressure;  relative  aptitude  of  different 
regions  in  appreciating  it ;  variable  sensation  according  to  the  form  of 
the  body  and  the  extent  of  its  surface. — Sensation  of  temperature,  variable 
according  to  the  temperature  of  the  skin,  the  density  of  bodies,  and  the 
surface  in  contact :  identical  sensation  from  contact  with  a  body  very  hot 
and  very  cold;  relative  sensibility  of  different  regions  to  temperature. — 
The  touch;  its  delicacy.  —  The  touch  compared  with  the  other  senses; 
illusions  of  touch;  persistence  of  tactile  impressions,  sensations  from  in- 
ternal or  subjective  causes;  causes  which  modify  feeling. 


Touch  and  feeling. — Tactile  sensations,  like  all  others,  are 
more  or  less  complete  according  as  the  attention  is,  or  is  not, 
directed  to  them.  The  contact  of  a  foreign  body  with  any 
sensitive  portion  of  the  organism  is  revealed  to  us  \)j  feeling, 
and  it  is  by  touch  that  we  discover  the  form,  resistance,  and 
temperature  of  this  body.  Feeling  may  be  involuntary,  touch 
is  an  act  of  the  will;  there  is  therefore  the  same  difference 
between  feeling  and  touch  that  there  is  between  seeing  and 
looking;  between  hearing  and  listening,  scenting  an  odour  and 
smelling  it,  perceiving  a  flavour  and  tasting  it. 

We  must  also  distinguish  between  impressions  due  to 
general  sensibility  and  tactile  sensations  proper;  thus,  if  we 
knock  the  elbow  we  feel  an  acute  pain  along  the  course  of 
the  ulnar  nerve,  but  the  impression  produced  on  the  skin  is 
perfectly  distinct  from  this  deeper  suffering  when  not  entirely 
masked  by  it.  It  is  the  same  in  sensations  resulting  from  a 
shock  to  the  right  hypochonder  which  produces  a  pain  in  the 
liver.  All  the  tissues  which  receive  nerves  of  sensation  may 


2l8  THE    HUMAN    BODY. 

be  the  seat  of  impressions  which  may  be  referred  to  the 
general  sensibility,  and  which  are  for  the  most  part  painful; 
impressions  on  the  sense  of  touch  are  only  produced  in 
certain  tissues  specially  endowed  with  this  sense.  General 
and  tactile  sensibility  are  independent  of  each  other,  and 
they  are  not  developed  proportionally;  as,  for  instance,  the 
palmar  surface  of  the  ringers  is  endowed  with  an  exquisite 
sense  of  feeling,  but  it  is  almost  insensible  to  a  blow  which 
would  be  very  painful  to  the  cheek,  in  which  this  sense  is 
much  less  developed. 

Organ  of  touch. — Touch  has  its  seat  in  the  skin  throughout 
its  whole  extent,  and  in  some  of  the  mucous  membranes.  It 
is  by  the  nervous  papillae  containing  the  tactile  corpuscles 
that  the  impression  is  perceived,  and  the  tactile  sensibility  of 
any  region  is  in  proportion  to  the  number  of  nervous  papillae 
existing  in  it. 

We  receive  three  distinct  impressions  at  a  time  by  the 
sense  of  touch — that  of  contact  from  a  foreign  body,  that  of 
the  pressure  which  it  exercises  on  the  skin,  and  that  of  its 
relative  temperature. 

The  sensation  of  contact  is  not  equally  distinct  and  precise 
in  all  parts  of  the  body,  and  the  reason  of  this  we  will 
endeavour  to  explain.  If  we  apply  simultaneously  the  two 
points  of  a  compass  to  the  skin,  they  must  be  more  or  less 
separated  according  to  the  region  experimented  on,  in  order 
that  their  contact  may  cause  one  or  two  distinct  sensations, 
and  we  may  in  this  way  measure  the  delicacy  of  the  sense  at 
any  given  point  on  the  skin.  It  is  evident  that  the  less 
sensitive  the  skin  is,  the  more  widely  we  must  separate  the 
points  of  the  compass  to  produce  a  double  sensation. 
E.  Weber  after  many  experiments  classes  the  regions  in  the 
order  of  their  sensibility  as  follows : — The  tip  of  the  tongue 
gives  a  double  sensation  when  the  feet  of  the  compass  are 
separated  about  half  a  line ;  the  palmar  surface  of  the  ends 
of  the  fingers,  one  line;  the  red  surface  of  the  lips  and  the 
surface  of  the  second  joint  of  the  fingers,  two  lines;  the  end 
of  the  nose  and  the  palm  of  the  hand  near  the  fingers,  three 
lines;  the  back  and  edges  of  the  tongue  at  about  an  inch 
from  the  tip,  and  the  skin  of  the  lips,  four  lines;  the  palm 


RELATIVE    ACUTENESS    OF    SENSE    OF   TOUCH.  2 19 

of  the  hand,  the  cheek,  and  the  eyelids,  five  lines;  the 
palate,  six  lines;  the  prominence  of  the  cheek,  and  the  sole 
of  the  foot  near  the  great  toe,  seven  lines;  the  back  of  the 
hand  near  the  fingers,  eight  lines ;  the  gums,  nine  lines ;  the 
lower  portion  of  the  forehead,  ten  lines;  the  lower  part  of 
the  occiput,  twelve  lines;  the  back  of  the  hand,  fourteen 
lines;  the  throat  under  the  jaw,  fifteen  lines;  the  shoulder, 
fore-arm,  and  knee,  eighteen  lines;  the  chest  over  the 
sternum,  twenty  lines ;  the  loins,  the  upper  part  of  the  back, 
and  the  neck  on  the  line  of  the  spine,  twenty-four  lines; 
the  middle  of  the  back,  of  the  neck,  of  the  arm,  and  of  the 
thigh,  thirty  lines.  ' 

Gratiolet  found  by  oft-repeated  experiments  that  the  dis- 
tances recognized  by  the  pulp  of  the  fingers  might  be  very 
much  less.  By  touching  two  points  on  the  same  papillary 
ridge  on  the  pulp  of  the  last  joint  of  the  middle  finger,  sepa- 
rated only  by  the  orifice  of  a  sudoriferous  duct,  the  two  sen- 
sations were  plainly  distinguished  at  the  distance  of  less  than 
one  quarter  of  a  line. 

The  experiments  of  Valentin,  on  the  other  hand,  prove 
that  tactile  sensibility  varies  from  single  to  double  in  cor- 
responding regions  in  different  individuals;  we  can  only 
accept  the  measurements  of  Weber,  therefore,  as  indicating 
the  relative  sensibility.  And  lastly,  we  are  indebted  to  M. 
Belfield-Lefevre  for  the  experiments  which  led  him  to  the 
following  conclusions.  The  distance  between  two  points  of 
contact  is  better  appreciated,  if  these  points  are  placed  on  a 
line  transverse  to  the  axis  of  the  body,  than  when  on  a  line 
parallel  to  it  or  longitudinal.  According  to  Weber,  on  the 
ends  of  the  fingers,  and  on  the  tip  of  the  tongue,  the  distance 
is  better  appreciated  on  a  longitudinal  than  on  a  transverse 
line.  The  distance  between  two  points  of  contact,  distinct 
and  simultaneous,  is  greater  in  proportion  to  the  delicacy  of 
feeling  in  the  region  experimented  on;  it  seems  to  be  greater 
also  when  the  contact  takes  place  successively  in  the  two 
points,  than  when  it  takes  place  simultaneously,  and  greater 
also  if  the  two  contacts  are  separated  by  a  longer  interval  of 
time.  If  the  two  points  of  contact  are  separated  by  the 
median  line,  the  distance  between  them  seems  greater  than 


220  THE    HUMAN    BODY. 

if  they  are  placed  on  the  same  side  of  the  body. — If  two 
points  are"  touched,  which  are  subject  to  variation  from  func- 
tional displacement,  the  eyelids. or  the  lips  for  example j  the 
distance  is  greater  than  if  the  two  contacts  take  place  on  one 
eyelid,  or  one  lip.— This  sense  is  also  increasingly  developed 
on  the  surface  of  the  limbs  in  proportion  to  the  distance 
from  the  body. 

The  sensation  of  contact  varies  according  as  it  results  from 
a  simple  application  of  a  foreign  body  to  the  skin,  or  from  a 
shock,  or  a  succession  of  shocks  repeated  at  short  intervals, 
like  that  which  produces  vibration  in  a  body.  In  the  latter 
case  the  region  of  contact  receives  a  shock  in  proportion 
to  the  intensity  of  the  vibrations;  as  when  we  touch  the  skin 
with  a  timing  instrument  while  vibrating,  or  if  we  grasp  a 
vibrating  metallic  body  or  wooden  rod,  or  close  the  lips 
against  the  reed  of  a  basoon  while  it  is  being  blown  into,  it 
produces  on  the  surface  in  contact  an  impression,  varying 
from  a  painful  shock  to  a  simple  tickling  or  pleasurable  sen- 
sation. It  is  a  sensation  of  the  same  nature,  though  diffused 
through  the  whole  body,  that  we  feel  from  the  vibrations  im- 
pressed on  the  atmosphere  by  the  explosion  of  artillery,  the 
roll  of  thunder,  or  the  ringing  of  a  great  bell.  The  sense  of 
touch  then  gives  us  an  idea  of  the  sonorous  waves  which 
excite  the  auditory  nerve,  and  furnishes  us  with  the  proof, 
that  the  same  cause  acts  differently  on  the  special  nerves  of 
the  different  senses.  In  fact,  the  nervous  papillae  of  touch 
transmit  a  sensation  of  motion  and  of  shock;  the  tympanum 
perceives  neither  tickling  nor  shock,  the  impression  which  it 
transmits  to  the  auditory  nerve  is  not  that  of  a  vibratory 
movement,  but  of  the  sound  which  results  from  it. 

The  sensation  of  pressure  is  distinctly  perceived  by  touch; 
but  we  must  distinguish  between  the  pressure  of  a  body 
against  the  skin,  and  the  resistance  which  this  body  offers  to 
a  muscular  effort  tending  to  displace  it.  If  when  the  hand 
is  supported,  and  a  weight  placed  in  it,  no  effort  is  made  to 
raise  it,  and  the  muscles  remain  inactive,  we  feel  a  sensation 
of  pressure,  the  force  of  which  may  be  judged  of  with  more 
or  less  exactness;  but  the  moment  we  endeavour  to  appre- 
ciate the  weight  the  sensation  becomes  complex,  and  we 


SENSATION    OF    PRESSURE.  221 

have  the  idea  of  pressure,  and  that  of  the  muscular  effort 
which  we  oppose  to  it;  and  great  attention  is  necessary  to 
prevent  an  instinctive  contraction  of  the  muscles  of  the  hand 
to  resist  the  weight  with  which  it  is  charged.  We  must  also 
take  into  account  habit  and  the  relative  strength  of  the  hands; 
as  the  right,  which  is  generally  more  used  than  the  left; 
may  be  less  sensitive  to  pressure,  and  appreciate  its  degree 
less  exactly. 

Those  portions  of  the  skin  where  the  touch  is  most  acute, 
and  where  two  points  of  contact  are  perceptible  at  slight 
distances,  are,  according  to  Belfield-Lefevre,  those  which 
estimate  most  correctly  the  degree  of  pressure;  as  the  lips, 
the  palmar  surface  of  the  fingers,  the  under  surface  of  the 
toes,  and  the  skin  of  the  forehead,  are  better  endowed  in 
this  respect  than  the  rest  of  the  body.  But  neither  touch 
nor  pressure  alone  can  give  an  exact  notion  of  the  weight, 
we  must  support  the  body  on  which  the  experiment  is  made 
by  muscular  effort:  the  inequality  of  the  two  hands  in  this 
respect  is  so  well  known,  that  we  use  one  and  the  other 
alternately  in  order  to  ascertain  correctly  the  weight  of  the 
object.  It  is  estimated  that  pressure  alone  will  not  enable 
us  to  appreciate  more  than  an  eighth  of  difference  between 
two  weights,  but  by  lifting  we  can  appreciate  a  sixteenth. 

The  form  of  bodies  also  influences  the  sensation  of  pres- 
sure; when  an  object  with  only  a  small  surface  is  applied  to 
the  skin  the  pressure  seems  greater  than  when  it  is  spread 
over  a  greater  extent;  and  it  may  even  become  painful  when 
supported  on  a  restricted  point;  thus,  the  weight  which  we 
carry  with  ease  on  the  whole  breadth  of  the  shoulder,  is  in- 
tolerable when  resting  only  on  one  of  its  angles.  A  truncated 
cone  laid  on  the  forehead  seems  heavy  or  light  according  as 
it  rests  on  its  smaller  or  larger  base.  Soldiers  and  travellers 
know  very  well  that  they  cannot  with  impunity  exchange  the 
broad  bands  of  their  knapsacks  for  narrow  straps  or  cords. 
It  is  unnecessary  to  remark,  that  if  the  weight  be  distributed 
over  a  large  surface,  each  point  of  that  surface  supports  but 
a  fraction  of  the  entire  weight;  the  whole  mass,  on  the  con- 
trary, presses  on  a  limited  space. 

Sensation  of  temperature. — We  recognize  by  contact  with  a 


222  THE    HUMAN    BODY. 

body  whether  its  temperature  is  the  same,  or  whether  it  is 
higher  or  lower  than  the  point  of  skin  which  touches  it;  in 
other  words,  touch  gives  us  an  idea  of  the  relative  tempera- 
ture of  bodies.  But  the  sensation  may  change  in  a  few 
moments,  as  the  object  in  contact  with  the  skin  rapidly  im- 
parts or  borrows  heat;  and  if  it  is  warmer  or  colder  than  the 
skin,  an  equilibrium  is  soon  established  when  the  difference 
is  inconsiderable.  And  the  same  body  may  produce  a  sensa- 
tion of  cold  or  heat  successively  without  change  of  tempera- 
ture, according  as  the  surface  of  the  skin  at  the  moment  of 
contact  is  warm  or  cold;  thus,  if  we  take  a  bath  in  water 
cooler  than  the  air,  the  temperature  of  the  air,  which  seemed 
low  on  entering  the  bath,  appears  warm  when  we  come  out 
a  few  minutes  after.  It  is  for  the  same  reason  that  we  find 
the  air  of  a  cellar  cool  in  summer,  and  warm  in  winter, 
although  it  has  not  varied. 

The  sensation  is  marked  in  proportion  to  the  conducting 
quality  of  the  object  in  contact  with  the  skin.  Air  seems 
warmer  than  water  at  the  same  temperature,  because  the  air 
being  a  worse  conductor  of  heat  takes  less  from  the  skin  in  a 
given  time.  Air  in  motion,  by  exciting  evaporation,  causes 
a  very  sensible  loss  of  heat,  as  every  one  knows;  and  the 
atmosphere  also,  which  seems  very  cold  when  the  wind  blows, 
grows  warmer  apparently  when  the  wind  ceases,  or  when  we 
are  sheltered  from  it. 

The  contrary  effect  from  that  caused  by  pressure  is  here 
seen;  the  sensation  is  marked  in  proportion  to  the  extent  of 
surface.  The  whole  hand  appreciates  the  temperature  better 
than  a  single  finger;  and  a  body  of  a  given  temperature, 
applied  over  a  large  surface,  will  give  a  sensation  of  more 
intense  heat  than  a  warmer  body  which  touches  only  a  small 
portion  of  skin.  We  can  easily  understand  that  the  skin 
absorbs  in  a  given  time  more  heat  by  a  surface  four  inches 
square,  than  by  one  only  one  inch  square,  and  the  impression 
transmitted  to  the  brain  in  this  experiment  represents  rather 
the  sum  of  the  heat  absorbed  from  all  parts  of  the  surface  in 
contact,  than  the  temperature  of  the  body  with  which  the 
experiment  is  made. 

When  we  touch  a  body  of  a  lower  temperature,  the  same 


SENSATION    OF   TEMPERATURE.  223 

sensation  is  produced  as  when  we  touch  one  at  a  high  tem- 
perature. Contact  with  a  ball  of  frozen  mercury  causes 
a  burning  sensation,  the  same  as  that  of  iron  heated  to 
100°  C.  (212°  R),  though  we  know  that  mercury  freezes  at 
— 40°  C.  ( — 40°  F. )  Voyagers  in  the  Polar  regions  are  com- 
pelled to  envelop  the  metallic  portions  of  their  instruments  in 
non-conducting  substances,  so  as  to  be  able  to  handle  them 
with  impunity. 

The  skin  and  the  mucous  membranes  do  not  appreciate 
differences  of  temperature  with  equal  nicety  in  every  portion 
of  their  surface,  and  the  regions  which  are  most  sensitive  to 
contact  are  not  those  which  best  indicate  the  temperature. 
The  palmar  surface  of  the  fingers,  the  tongue,  and  the  lips, 
are  less  impressionable  in  this  respect  than  the  skin  of  the 
cheeks,  eyelids,  elbow,  and  the  pituitary  membrane.  We 
may  perhaps  attribute  this  relative  insensibility  in  the  hand, 
and  the  mucous  membrane  of  the  cheeks,  to  the  habit  of 
contact  with  warm  bodies.  The  hand  becomes  rapidly 
inured  to  hold  objects  hot  enough  to  cause  a  painful  sensa- 
tion to  persons  unaccustomed  to  it.  We  see  this  in  chemists, 
blacksmiths,  and  others.  The  skin  need  not  necessarily  be 
thickened,  although  this  condition  also  decreases  the  sensi- 
bility. We  often  see  persons  of  mature  age  bear  without 
pain  the  contact  of  food  so  hot  that  younger  people  could 
not  swallow  it.  The  mucous  membranes  of  the  oesophagus 
and  the  stomach  are  more  sensitive  in  this  respect  than 
that  of  the  mouth ;  but  when  the  food  is  held  immovable  for 
a  few  seconds  between  the  palate  and  the  tongue,  the  heat 
is  absorbed,  and  the  food  or  drink  may  be  swallowed  with 
impunity. 

It  is  clear  from  the  preceding  remarks  that  the  sense  of 
touch  is  an  unreliable  thermometer;  it  is  sufficient,  however, 
to  guide  us  in  matters  relating  to  health,  and  in  regard  to 
external  objects,  especially  when  we  permit  its  full  develop- 
ment by  touch. 

The  hand  is  the  principal  means  of  exercising  the  touch. 
The  organization  of  this  admirable  instrument,  its  numerous 
articulations,  the  freedom  and  variety  of  its  movements,  the 
tactile  sensibility  which  is  so  fully  developed  in  the  palmar 


224  THE    HUMAN    BODY. 

surface  of  the  fingers  enables  us  to  obtain,  by  means  of  it, 
ideas  of  the  form  and  relative  situation  of  objects,  of  their 
motion,  their  resistance,  their  weight,  their  solid  or  fluid  con- 
dition, of  their  temperature,  &c.  The  hand  grasps  objects, 
moves  over  their  surface,  follows  their  outline,  measures  their 
distance  and  their  extent,  as  far  as  the  length  of  the  lever 
of  which  it  forms  the  extremity  will  permit.  By  the  aid  of 
this  lever  it  raises  bodies,  estimates  their  weight,  their  firm- 
ness, and  their  elasticity.  In  touching  them  with  the  ends 
of  the  fingers  it  perceives  the  details  of  their  form  and  their 
relative  value.  We  have  seen  of  how  great  importance  deli- 
cacy of  touch  is  to  the  artist,  it  is  no  less  precious  to  the 
physician,  and  it  renders  him  service  which  he  asks  in  vain 
of  any  other  sense.  It  is  by  the  touch  that  he  arrives  at  a 
knowledge  of  the  state  of  the  circulation,  the  existence  of 
fluids  in  the  tissues,  and  their  normal  or  morbid  consistence. 

By  exercise  the  touch  attains  extreme  delicacy.  The 
blind  learn  to  read  with  facility  from  letters  printed  in  relief, 
and  to  execute  certain  work  with  tools.  Saunderson,  pro- 
fessor of  mathematics  in  the  university  of  Cambridge,  was 
blind  from  his  cradle,  but  he  had  attained  to  such  exquisite 
perfection  of  touch,  that  in  a  set  of  medals  he  could  dis- 
tinguish the  genuine  from  the  counterfeit  pieces,  though  the 
latter  were  so  well  executed  as  to  deceive  a  connoisseur 
judging  by  sight.  He  felt,  by  the  impression  of  the  air  on 
his  face,  when  he  was  passing  near  a  tree.  It  is  said  that 
Jean  Gonnelli,  a  blind  sculptor,  could  model  in  clay  an 
exact  copy  of  a  statue  the  outline  of  which  he  had  studied 
by  touch,  but  doubtless  we  must  take  this  anecdote  with 
some  allowance  for  exaggeration. 

However  this  may  be,  the  touch  has  been  from  the  earliest 
antiquity  an  object  of  the  most  enthusiastic  admiration  to 
naturalists.  It  has  been  considered  as  the  most  exact  and 
the  most  infallible  of  the  senses,  able  to  control  their  testimony 
and  rectify  their  errors.  It  has  been  placed  in  the  front 
rank,  and  held  up  as  a  type  of  which  the  others  are  only  the 
modifications.  Buflbn  says,  "It  is  by  the  touch  alone  that 
we  acquire  complete  and  accurate  knowledge ;  it  is  this  sense 
which  rectifies  all  the  other  senses,  which  might  only  delude 


COMPARISON  BETWEEN  TOUCH  AND  OTHER  SENSES.  225 

us  and  make  us  err,  if  it  did  not  guide  our  judgment."  But 
BufTon  thought  that  "the  difference  between  our  senses 
results  only  from  the  more  or  less  external  position  of  the 
nerves,  and  from  their  greater  or  less  number  in  the  parts 
which  constitute  the  organs."  The  illustrious  naturalist  did 
not  recognize  the  special  functions  of  the  sensitive  nerves; 
the  sensations  of  colours,  of  odours,  of  flavours,  and  of  sounds, 
were  for  him  only  tactile  impressions.  How  could  we  admit 
that  feeling  could  guide  us  in  judging  of  the  colour  of  objects, 
of  their  taste,  their  odour,  or  their  sound !  Even  while  ad- 
mitting that  we  can  compare  the  excitation  of  the  skin  by 
contact  to  that  of  the  retina  by  the  luminous  waves,  it  is  not 
the  less  impossible  to  establish  the  least  analogy  between 
touch  and  sight,  since  the  retina  is  insensible  to  contact,  and 
as  well  as  the  optic  nerve,  conveys,  not  a  tactile,  but  a 
luminous  impression  to  the  brain.  As  for  the  other  senses, 
if  air  in  vibration  comes  in  contact  with  the  tympanum  of 
the  deaf  man  he  perceives  no  sound,  though  he  is  sensible  of 
contact  from  foreign  bodies  on  the  tympanum ;  if  odoriferous 
or  savoury  bodies  come  in  contact  with  the  pituitary  mem- 
brane or  with  the  tongue  of  a  man  who  has  lost  the  sense  of 
smell  or  taste,  he  perceives  neither  odours  nor  flavours,  al- 
though he  is  perfectly  aware  of  the  presence  of  a  foreign 
body  in  the  nose  or  mouth. 

The  touch  therefore  cannot  replace  the  other  senses, 
though  it  sometimes  corrects  their  impressions,  but  it  needs 
to  be  constantly  controlled  and  completed  in  the  sensations 
which  it  produces  in  us.  If  it  enables  us  to  learn  form, 
it  is  the  eye  which  tells  us  of  colour,  and  often  perfects  or 
corrects  our  notions  of  distance,  extent,  and  even  of  form; 
as  for  instance,  we  distinguish  less  easily  with  the  touch  than 
with  the  eye  a  sphere  from  an  ellipsoid  which  is  nearly 
spherical.  And  besides  it  is  when  the  touch  has  been  exer- 
cised under  the  control  of  the  sight  that  it  furnishes  us  with 
the  most  exact  ideas,  for  its  results  are  then  confirmed  by 
those  which  we  possess  already  in  regard  to  time,  motion, 
space,  and  the  normal  position  of  bodies,  &c.  Yet  even  in 
these  conditions  the  sense  of  feeling  may  be  the  source  of 
error.  M  tiller  says,  and  rightly  too,  that  by  touch  we  feel  not 

15 


226 


THE    HUMAN    BODY. 


the  object  which  touches  us,  but  that  part  of  the  tegument 
where  the  contact  takes  place  and  the  impressions  which 
it  receives.  The  idea  of  external  objects  given  by  touch 
then  is,  when  completely  analyzed,  the  possibility  of  distin- 
guishing the  different  parts  of  the  body  as  occupying  a 
different  place  in  space.  The  result  is,  that  if  the  parts  of 
our  bodies  are  momentarily  in  an  abnormal  condition,  we 
receive,  notwithstanding,  the  sensation  in  the  relative  order 
that  the  regions  from  which  these  sensations  emanate  pre- 
serve in  a  normal  condition.  If,  for  example,  we  cause  .a 
ball  to  revolve  between  two  fingers  of  the  same  hand,  we 
have  the  sensation  of  a  single  body  touching  these  two 
fingers;  but  if  we  cross  the  fingers  and  place  the  ball  between 


Fig-  43- 


their  extremities,  the  sensation  is  that  of  two  balls,  each  one 
rolling  in  contact  with  one  of  the  fingers. 

The  sensations  of  touch  are  somewhat  persistent,  especially 
when  the  tactile  impression  is  joined  to  that  of  general  sensi- 
bility. Thus  when  we  have  carried  a  burden  on  the  shoulder, 
or  when  any  part  of  the  body  has  been  subjected  to  great 
and  prolonged  pressure,  we  still  perceive  the  sensation  some- 
time after  the  weight  is  removed  and  the  pressure  has  ceased, 
but  in  such  cases  the  tissues  subjacent  to  the  skin  take  part 
in  the  sensation  as  well  as  the  skin  itself. 

The  organ  of  touch  may  also  be  the  seat  of  impressions 
which  are  subjective,  or  which  arise  from  internal  causes, 
physical  or  moral.  The  sight  of  a  striking  spectacle  or  the 
emotion  caused  by  a  narrative  produces  in  soire  persons  a 


MODIFICATIONS    OF    FEELING.  227 

marked  sensation  of  cold ;  the  idea  of  shivering  causes  an  im- 
pression which  resembles  it,  and  the  fear  of  tickling  is  suffi- 
cient to  produce  its  effects. 

Feeling  is  modified  by  various  influences;  cold,  or  san- 
guineous congestion  resulting  from  violent  exercise,  diminishes 
or  suppresses  for  a  time  the  sensibility  of  the  skin ;  certain 
occupations,  by  thickening  the  epidermis,  destroy  the  delicacy 
of  the  touch;  and  lastly,  age  diminishes  the  cutaneous  per- 
spiration, the  epidermis  dries  up,  and  the  skin  no  longer  has 
the  suppleness  and  elasticity  which  renders  the  touch  so 
delicate  in  youth. 

Tactile  sensibility  is  often  intensified  by  disease,  and  some- 
times modified,  suspended,  or  destroyed.  We  see  this  in 
trances  which  supervene  after,  or  are  provoked  under,  the  in- 
fluence of  certain  nervous  affections.  Charlatanism,  even  in 
our  day,  avails  itself  of  this  phenomenon,  which  we  confine 
ourselves  to  simply  mentioning  here. 


CHAPTER    XVI. 


Voice  and  speech. — Organ  of  voice ;  larynx,  cavity  of  the  larynx, 
glottis,  vocal  cords ;  the  larynx  at  different  ages  and  in  different  sexes. — 
Physiology  of  the  larynx;  mechanism  of  the  voice;  opinions  as  to  the 
formation  of  the  voice.  — Galen,  Fabricins  Acquapendente,  Dodart, 
Ferrein,  Biot,  Milller,  Savart,  Masson,  and  Longet. —  Theories  founded 
071  laryngoscopic  observations. — Formation  of  sounds  in  whistling. — 
Voice ;  speaking  voice,  mechanism  of  articulate  sounds,  vowels  ^  con- 
sonants, timbre  of  the  vowels;  the  tongne  as  an  organ  of  pronunciation^ 
— Singing;  chest  voice,  falsetto  voice,  mixed  voice;  different  theories  on  the 
formation  of  the  falsetto :  Milller,  M.  Segond,  M.  Longet,  M.  Fournie, 
M.  Bataille,  M.  Mandl.  —  Timbres  of  the  voice:  high  pitch,  grave  pitch. 
—  Compass  of  voices :  bass,  baritone,  tenor,  contralto,  mezzo-soprano, 
soprano.  —  Ventriloquy. 

The  larynx. — The  organ  of  the  voice  is  a  sort  of  a  cartilagin- 
ous tube  composed  of  movable  pieces  articulated  together,  per- 
fectly symmetrical,  wider  and  triangular  at  its  upper  portion, 
which  opens  into  the  pharynx,  cylindrical  at  its  lower  portion, 
where  it  is  continuous  with  the  trachea.  It  is  placed  in  the 
anterior  and  •middle  portion  of  the  neck  and  below  the 
hyoid  bone,  to  which  it  is  united  by  muscles  and  ligaments, 
and  in  consequence  it  follows  the  movements  of  the  hyoid 
bone  and  the  tongue,  rising  and  falling  with  them.  Its 
movements  are  connected  with  deglutition,  the  acuteness 
and  gravity  of  sounds  emitted,  and  with  respiration  according 
as  it  is  diaphragmatic  or  clavicular  (see  Respiration,  p.  97). 

Five  cartilages  form  the  skeleton  of  the  larynx;  they  are 

1.  The  cricoid  cartilage  (cricos,  a  ring);  it  is  situated  at  the 
base  of  the  organ,  and  is  attached  to  the  first  ring  of  the 
trachea. 

2.  The  thyroid  cartilage  (thyreos,  a  buckler),  which  is  com- 
posed of  two  quadrilateral  plates,  joined  together  in  front 


THE    LARYNX. 


and  on  the  median  line.  This  cartilage  protects,  as  its  name 
indicates,  the  organ  of  the  voice.  In  front  a  ligament 
attaches  its  lower  border  to  the  cricoid  cartilage,  with  which 
it  is  articulated  behind;  its  anterior  surface  presents  at  the 


Fig.  44.— Section  of  larynx  in  the  median  line. 


A.  Epiglottis,  in  front  of  which  the 

hyoid    bone    and    base    of   the 
tongue  are  seen. 

B.  Thyroid  cartilage. 

C.  Arytenoid  cartilage. 


E.  Anterior  portion  of  cricoid 

cartilage. 

F.  Vocal  cord  of  right  side. 

G.  Ventricle  of  the  larynx. 
H.   Rings  of  the  trachea. 


D.  Posterior  portion  of  cricoid  cartilage.        I.    Trachea. 

top  an  angular  sloping  protuberance,  which  is  more  marked 
in  man  than  in  woman.  It  forms  the  projection  on  the  front 
of  the  neck  which  is  called  "Adam's  apple."  The  upper 
border  is  united  to  the  hyoid  bone  by  a  membrane  and 
ligaments. 

3.  The  two  aryteiwid  cartilages  (arutaina,  a  funnel);  they- 


230  THE    HUMAN    BODY. 

form  the  posterior  and  superior  wall  of  the  larynx,  and  come 
together  behind  in  the  shape  of  the  lip  of  a  ewer;  they  arti- 
culate with  the  cricoid  cartilage,  and  are  united  to  the  thyroid 
by  muscles  and  ligaments. 

4.  The  epiglottis  (epi,  added  to,  glotta,  the  tongue)  is  a  sort 
of  cartilaginous  valve,  very  elastic  and  mobile,  situated  a 
little  below  the  base  of  the  tongue,  and  attached  to  the  supe- 
rior border  of  the  thyroid  cartilage.  Its  function  is  to  cover 
exactly  the  superior  opening  of  the  larynx  during  deglutition, 
so  as  to  prevent  the  introduction  of  the  food  into  the  air- 
passages.  When  the  tongue  is  brought  well  forward,  and 
the  base  depressed,  in  some  individuals  the  summit  of  the 
epiglottis  is  visible. 

Numerous  muscles  attach  the  larynx  to  the  sternum,  to  the 
hyoid  bone,  and  by  this  last  to  the  shoulder-blade,  to  the 
tongue,  and  to  the  lower  jaw;  these  muscles  are  called  ex- 
trinsic^ and  move  the  larynx  as  one  piece.  Others,  called 
intrinsic  muscles  of  the  larynx,  combine  to  form  its  walls, 
and  to  modify  its  diameter  by  acting  on  the  cartilages,  and 
assist  in  the  functions  of  the  glottis.  Lastly,  the  arytenoid 
cartilages  are  united  by  ligaments  to  the  epiglottis,  or  to  the 
thyroid  cartilage;  these  last,  the  thyro-arytenoid  ligaments 
form,  with  the  muscles  of  the  same  name  and  with  the  mucous 
membrane,  the  vocal  cords,  of  which  we  proceed  to  speak. 

The  cavity  of  the  larynx,  or  its  internal  surface,  does  not 
correspond  in  form  and  dimensions  with  the  external  surface; 
it  is  cylindrical  at  the  bottom,  triangular  at  the  top;  the 
dimensions  of  the  lower  part  are  invariable,  while  those  of 
the  upper  portion,  on  the  contrary,  are  variable  in  form,  from 
the  mobility  of  the  epiglottis,  of  the  arytenoid  cartilages,  &c. 
About  the  middle  of  its  height  the  laryngeal  cavity  presents 
on  each  side  a  fold  formed  by  the  thyro-arytenoid  muscles  and 
lower  ligaments  of  the  same  name,  and  the  mucous  mem- 
brane; these  resemble  two  ribbons  of  a  white  colour  tinged 
with  rose,  running  horizontally  from  front  to  back,  attached 
by  their  external  border  and  their  extremities  to  the  wall  of 
the  larynx,  free  on  the  surface  and  internal  border,  leaving 
an  opening  between  them  which  is  linear,  elliptic,  or  trian- 
gular, according  to  the  moment  when  it  is  observed,  and 


GLOTTIS.      VOCAL   CORDS.  23! 

whether  we  see  the  whole  or  only  the  two  anterior  thirds. 
This  opening  permits  the  passage  of  the  air  into  and  out  of 
the  chest,  it  is  called  the  glottis,  the  folds  which  circumscribe 
it  have  been  called  the  vocal  cords.  About  one-third  of  an 
inch  higher  up  there  are  two  other  similar  but  less  prominent 
folds,  they  are  formed  by  the  superior  thyro-arytenoid  liga- 
ments, and  are  designated  by  this  name,  or  by  that  of  the 
superior  vocal  cords  (see  fig.  44,  p.  229).  The  space  between 
them  has  been  called  the  superior  glottis,  it  is  larger  than  the 
glottis  proper,  and  does  not  resemble  it  in  form  when  exam- 
ined by  the  aid  of  the  laryngoscope.  Before  this  instrument 
was  invented  the  larynx  was  described  by  anatomists  as  they 
saw  it  in  the  dissecting-room,  hence  the  name  of  superior 
glottis,  and  the  likening  of  this  orifice  to  that  of  the  glottis. 

Between  the  vocal  cords  proper  and  the  superior  thyro- 
arytenoid  ligaments  there  is  on  each  side  a  depression;  these 
are  the  ventricles  of  the  larynx;  and  lastly,  a  little  above  these 
ligaments  is  the  stiperior  opening  of  the  larynx,  surmounted  in 
front  by  the  epiglottis,  which  is  lowered  upon,  and  covers  it 
completely  during  deglutition.  The  space  comprised  between 
the  glottis  and  the  superior  opening  of  the  larynx  is  called 
the  vestibule  of  the  glottis. 

Formerly  authors  were  divided  in  opinion  in  regard  to  the 
larynx;  some  gave  the  name  of  glottis  to  all  the  region 
between  the  level  of  the  inferior  and  that  of  the  superior 
vocal  cords,  others  applied  it  to  the  superior  glottis,  and 
others  again  to  the  inferior  glottis  only.  This  last  opinion, 
which  has  been  commonly  received  since  the  investigations  of 
Bichat  and  Boyer,  has  been  confirmed  by  the  laryngoscope, 
which  demonstrates  the  existence  of  a  single  glottis,  and  a 
single  pair  of  vocal  cords. 

The  internal  walls  of  the  larynx  are  lined  with  a  fibrous 
membrane,  constituted  in  part  by  yellow  elastic  tissue.  This 
membrane,  which  forms  the  thyro-arytenoid  and  aryteno-epi- 
glottic  ligaments,  is  covered  throughout  its  whole  extent  by 
a  mucous  membrane,  which  on  the  free  border  of  the  vocal 
cords  is  very  thin  and  transparent,  slightly  adherent,  and 
covered  with  an  epithelium  different  from  that  found  on  the 
rest  of  its  surface. 


232  THE    HUMAN    BODY. 

The  larynx  is  but  slightly  developed  in  early  infancy,  and 
does  not  differ  in  its  dimensions  in  the  two  sexes;  and  the 
characteristics  of  the  voice  are  the  same  also.  From  the  t 
third  to  the  twelfth  year  this  organ  remains  nearly  stationary; 
but  about  the  fourteenth  year  it  almost  doubles  in  size  in  the 
boy,  and  the  voice  takes  a  masculine  character.  This  evolu- 
tion is  rapid,  and  is  nearly  accomplished  in  the  course  of  a 
year,  though  the  larynx  is  not  perfectly  developed  till  the 
twenty-fifth  year.  In  girls  it  augments  about  a  third  in  size. 
The  larynx,  therefore,  of  an  adult  woman  is  smaller  than  that 
of  man,  its  angles  are  less  prominent,  and  the  glottis  is 
smaller.  These  differences  are  related  to  the  characteristic 
pitch,  compass,  and  power,  which  distinguish  the  voice  of 
man  from  that  of  woman. 

In  diaphragmatic  respiration  the  larynx  is  immovable;  but 
when  the  expansion  of  the  chest  extends  to  the  upper  ribs, 
the  sternum,  and  the  clavicle,  two  of  the  extrinsic  muscles 
of  the  larynx  assisting  in  the  elevation  of  the  sternum,  cause 
by  their  contraction  the  descent  of  the  larynx,  to  which  they 
are  attached  by  their  upper  extremities.  (See  Respiration, 

P-  97-)  . 

Physiology  of  the  larynx,  mechanism  of  the  voice. — Like  most 
physiological  questions,  that  of  the  emission  of  the  voice  is 
differently  explained  by  writers  on  that  subject.  In  order  to 
explain  its  functions,  the  larynx  has  been  compared  to  dif- 
ferent musical  instruments.  Gerdy  thought  "that  we  should 
do  better  to  endeavour  to  show  that  this  instrument  in  man 
has  no  resemblance  to  any  one  formed  by  art."  This,  doubt- 
less, is  true;  the  human  larynx  is  as  inimitable  in  its  perfec- 
tion as  it  is  admirable  in  the  results  it  produces;  but,  in 
comparing  the  most  ingenious  machines  of  this  character 
that  man  has  ever  constructed,  with  the  larynx,  we  do  pre- 
cisely what  Gerdy  recommends,  for  this  is  the  surest  means 
of  establishing  its  evident  superiority.  The  analogy  is  besides 
incontestable,  in  spite  of  the  distance  which  separates  an 
inert  mechanical  production  from  a  living  organic  apparatus, 
and  it  is  only  by  studying  the  formation  of  sounds  in  instru- 
ments that  we  can,  if  not  explain,  at  least  seek  to  comprehend 
their  formation  in  the  larynx. 


MECHANISM    OF    VOICE.  233 

The  vocal  apparatus  of  man  is  composed  of  the  lungs, 
acting  as  a  bellows;  the  trachea,  which  conducts  the  air  from 
the  lungs  to  the  larynx,  where  the  sound  is  formed;  and  of 
the  pharynx,  the  buccal,  and  nasal  cavities,  which  increase 
the  sounds  and  modify  their  character. 

The  air  driven  through  the  glottis  by  the  lungs  causes  a 
vibration  of  the  vocal  cords,  and  sound  is  produced;  it  is 
increased  by  passing  through  the  upper  part  of  the  larynx, 
the  mouth,  and  nasal  fossae;  it  acquires  more  or  less  volume, 
and  its  character  varies  according  as  these  cavities  are  more 
or  less  open  and  free;  but  it  does  not  change  its  nature  as 
regards  the  tone.  If,  for  example,  the  glottis  emits  a  C, 
it  may  be  heard  as  a  muffled,  a  natural,  or  a  nasal  sound, 
according  to  the  condition  in  which  the  cavities  are  through 
which  it  passes;  but  the  tone  does  not  change,  it  is  always 
aC. 

Savants  have  held  different  opinions  on  the  formation  of 
sounds  in  the  larynx,  and  upon  the  functions  of  the  constitu- 
ent parts  of  the  vocal  organs.  It  being  impossible  to  con- 
sider all  these  opinions,  or  the  many  experiments  which  have 
been  made,  the  physical  laws  upon  which  they  were  founded, 
or  which  were  opposed  to  them,  we  shall  confine  ourselves 
to  a  summary  explanation  of  a  few  of  them. 

We  may  be  permitted,  however,  first  to  quote  from  the 
Magasin  Pittoresque  an  anecdote  which  very  well  illustrates 
this  point  of  our  subject: — 

In  1798  Cuvier,  in  reading  an  essay  on  the  voices  of  birds 
before  the  Academy  of  Sciences,  remarked  that  some  phy- 
siologists considered  the  larynx  as  a  stringed  instrument, 
others  as  a  wind-instrument.  An  academician  spoke  and 
denied  this  distinction,  affirming  that  everybody  knew  that 
the  larynx  was  a  wind-instrument.  "You  are  in  error,"  im- 
mediately exclaimed  another  member,  "it  is  a  stringed  in- 
strument." 

These  two  theories  have  long  divided  philosophers. 

Galen  looked  upon  the  glottis  as  a  reed;  Fabricius  Acqua- 
pendente  gave  a  remarkable  description  of  the  larynx  in  the 
sixteenth  century;  he  recognized  the  glottis  as  the  essential 
organ  of  the  voice,  and  compared  its  action  to  that  of  an 


-234  THE    HUMAN    BODY. 

organ -pipe;  the  air  in  breaking  against  it  produced  the 
sound,  the  glottis  being  less  open  for  acute  than  for  grave 
sounds. 

Dodart  at  the  end  of  the  seventeenth  century,  after  hesi- 
tating between  the  vibration  of  the  air  or  the  vibration  of 
the  vocal  cords  as  the  origin  of  sound,  compares  the  glottis 
to  the  mouth-piece  of  a  hautboy.  This  great  physiologist,  in 
giving  successive  explanations,  differing  as  widely  as  possible 
from  each  other,  of  the  phenomena  of  the  voice,  has  advanced 
or  hinted  at  most  of  the  theories  which  have  been  projected 
since  his  time. 

In  1741  Ferrein  compared  the  vocal  cords  to  the  strings 
of  a  violin,  the  air  acting  as  the  bow. 

Biot  could  see  nothing  in  the  glottis  which  resembled  a 
vibrating  cord.  "The  simplest  principles  of  acoustics,"  said 
this  illustrious  physicist,  "are  sufficient  to  make  us  reject  this 
strange  opinion."  Miiller  advocated  the  theory  of  Ferrein 
against  that  of  Biot,  and  yet  he  admits  with  him  and  with 
Magendie,  Cagniard  de  la  Tour,  G.  Weber,  and  other 
learned  men,  that  the  glottis  is  a  reed  with  two  membranous 
lips  vibrating  under  the  action  of  the  air,  and  producing  the 
sound  by  their  vibrations. 

Sa.vart  compared  the  human  glottis  to  a  bird-catcher's 
whistle  surmounted  by  a  supply-pipe,  the  cavities  of  the 
whistle  being  represented  by  the  ventricles  of  the  larynx,  the 
openings  by  the  interval  between  the  vocal  cords.  The  air 
vibrated,  he  thought,  in  traversing  the  inferior  glottis,  and 
divided  into  two  columns  against  the  superior  vocal  cords, 
which  act  as  the  stop  in  an  organ-pipe,  one  of  these  columns 
of  air  in  vibrating  causes  the  resonance  of  the  air  in  the 
ventricles,  the  other  causes  the  vibration  of  the  air  in  the 
vocal  tube.  In  this  last  hypothesis  it  is  not  the  vibration  of 
the  vocal  cords,  but  that  of  the  air  which  produces  the  sound. 

The  theory  of  Savart  on  this  latter  point  has  been  admitted 
by  Longet  and  Masson.  They  believe  the  sound  is  pro- 
duced at  the  orifice  of  the  inferior  glottis  the  same  as  at  the 
mouth-piece  of  wind-instruments,  by  the  periodically  variable 
passage  of  the  air,  which  becomes  the  seat  of  a  vibratory 
movement.  The  inferior  vocal  cords  and  the  ventricles  are 


MECHANISM    OF   VOICE.  235 

necessary  for  voice ;  the  superior  vocal  cords  should  be  con- 
sidered simply  as  a  means  of  perfection  in  regard  to  the 
variation  and  modulation  of  sounds. 

Haller  thought  the  epiglottis  had  no  influence  on  voice, 
but  that  it  permitted  the  swelling  of  the  sounds  into  grave  or 
acute  without  changing  the  tone,  as  did  also  Magendie  and 
Biot.  Longet  thinks  that  it  assists  in  the  expulsion  of  the 
air  by  the  nasal  fossae  in  the  production  of  very  acute 
sounds,  and  that  it  may  contribute  to  the  timbre  of  the  voice. 

The  part  of  the  pharyngeal,  buccal,  and  nasal  cavities  in 
the  production  and  modification  of  sound  is  differently  stated 
by  different  authors.  Savart  thought  that  they  regulated  the 
height  of  vocal  sounds ;  they  have  been  considered  as  sup- 
plementary apparatus,  and  that  it  is  to  their  peculiar  reson- 
ance that  the  quality  of  the  voice  is  due. 

The  invention  of  the  laryngoscope,  by  enabling  us  to  see 
the  interior  of  the  larynx,  has  given  us  exact  notions  of  its 
function.  It  enables  us  to  verify  the  changes  of  form,  the 
appearance  of  the  glottis  at  different  ages,  and  during  the 
emission  of  the  voice.  This  method  of  studying  the  larynx 
has  resulted  in  late  years  in  works  of  the  greatest  interest. 

M.  Fournie  considers  the  larynx  as  a  membranous  reed- 
instrument,  and  the  mechanism  of  the  voice,  according  to 
this  learned  observer,  is  as  follows: — The  vocal  cords  pro- 
duce the  sound  by  their  vibration,  but  do  not  vibrate  in  their 
totality.  Fixed  in  front  and  at  the  back,  at  the  level  of  their 
free  border,  they  may  be  separated  by  the  air,  but  not  caused 
to  vibrate  in  their  entire  thickness,  while  the  mucous  mem- 
brane which  covers  their  free  border,  and  which  adheres  only 
very  slightly,  detaches  itself  under  the  influence  of  the  passing 
air,  and  thus  forms  the  free  vibrating  portion  of  the  reed. 
On  this  part  only  of  the  larynx  the  epithelium  of  the  mucous 
membrane  is  of  the  same  nature  as  that  of  the  membranes 
in  the  other  parts  of  the  organism  which  are  subjected  to 
constant  friction,  as  those  of  the  articulations  for  example, 
and  this  gives  it  the  power  of  resisting  the  friction  of  the  air 
and  of  the  vibrations  which  it  causes.  In  the  emission  of 
the  voice  the  vocal  cords  are  stretched  lengthwise  and 
breadthwise.  By  producing  mechanically  this  double  tension 


236  THE    HUMAN    BODY. 

of  the  vocal  cords  in  the  larynx  after  death,  M.  Fournie' 
obtained  all  the  notes  comprised  between  two  octaves. 

The  ventricles  of  the  larynx  are  contracted  and  almost 
effaced  during  the  emission  of  the  voice;  their  function  seems 
to  be  to  moisten  the  vocal  cords  with  a  mucous  fluid,  and 
to  aid  in  their  movements,  as  well  as  those  of  the  walls  of 
the  vestibule  and  glottis. 

The  superior  thyro-arytenoid  ligaments  adapt  the  tube 
formed  by  the  vestibule  of  the  glottis  to  the  sounds  emitted 
by  the  vocal  cords.  During  the  emission  of  sound  their 
borders  are  never  on  the  same  line  as  the  opening  of  the 
glottis;  sometimes  they  approach  the  vocal  cords,  sometimes 
they  almost  disappear,  or,  on  the  contrary,  enlarge  into  the 
vestibule  of  the  glottis  so  as  almost  to  fill  it.  By  experiments 
on  the  dead  subject,  M.  Fournie  has  proved  that  if  these 
ligaments  are  drawn  apart  during  the  emission  of  a  note  by 
the  larynx,  the  sound  is  lower  by  one  tone;  if  only  one  is 
drawn  aside  it  falls  a  semitone.  The  same  result  is  produced 
in  all  the  notes  comprised  in  an  octave. 

The  epiglottis  descends  and  nearly  closes  the  superior 
opening  of  the  larynx  in  grave  sounds,  and  rises  more  and 
more  as  the  sound  becomes  more  acute.  In  the  grave 
notes  the  soft  palate  permits  the  sounds  to  pass  through 
the  mouth  and  the  nasal  fossae,  and  in  proportion  as  the  voice 
is  elevated  it  rises  toward  the  posterior  orifice  of  the  nasal 
fossae,  so  as  to  prevent  the  echoing  of  the  sound  in  these 
cavities. 

The  nasal  fossae  give  exit  to  the  air  when  the  disposition 
of  the  vocal  tube  is  such,  in  the  formation  of  certain  letters, 
as  more  or  less  to  hinder  its  passage  through  the  mouth.  The 
isthmus  of  the  throat  and  the  mouth  have  no  influence  on 
the  note,  but  they  perfect  and  modify  its  character.  The 
trachea  and  bronchia,  as  well  as  the  vocal  tube,  resound  like 
a  harmonic  table,  of  which  each  part  corresponds  to  one  of 
the  notes  of  the  voice;  and  lastly,  the  intensity  of  the  sound 
is  in  direct  proportion  to  the  force  of  the  impulsion  of  the 
air,  to  the  extent  of  the  vocal  cords  put  in  vibration,  and  to 
their  tension. 

Formation  of  sounds  in  u>  hist  ling. — The  study  of  the  for- 


WHISTLING.  237 

mation  of  sounds  in  the  glottis  includes  that  faculty  which 
man  possesses  of  producing  the  sounds  of  whistling.  This 
.is  certainly  a  much  less  important  and  less  elevated  function; 
but  it  is  nevertheless  very  interesting  to  the  physiologist,  as 
it  evidently  nearly  resembles  that  of  the  voice  in  its  me- 
chanism. 

In  order  to  produce  the  sound  of  whistling,  the  lips  form 
a  real  glottis,  which  Dodart  has  named  the  labial  glottis.  The 
opening  between  the  lips  varies  in  form;  in  the  grave  tones  it 
is  nearly  round  in  shape,  and  at  its  maximum  in  diameter ;  in 
the  acute  sounds  it  becomes  elliptic,  and  is  reduced  to  a 
narrow  slit;  the  tongue  regulates  the  intonation,  by  approach- 
ing more  or  less  to  the  lower  front  teeth,  touching  them  in 
the  acute  sounds,  and  withdrawing  itself  in  the  grave  sounds. 
The  space  which  separates  the  lips  from  the  teeth  varies  also, 
in  the  same  relative  degree,  for  the  same  reason.  The  tongue 
sharpens  the  notes  as  in  flute-playing;  the  grave  sounds  may 
be  produced  in  drawing  in  the  air,  as  in  breathing;  in  short, 
the  sound  is  acute  or  intense  in  proportion  to  the  impulsion 
of  the  air  by  the  lungs. 

If  a  disk  of  cork  be  placed  between  the  lips,  about  one- 
fifth  of  an  inch  in  thickness,  with  a  hole  about  one  line 
in  diameter  in  the  centre,  the  sound  of  whistling  can  be  pro- 
duced through  this  aperture,  and  modulated  the  same  as 
with  the  lips.  Cagniard  de  la  Tour,  to  whom  we  are  in- 
debted for  this  experiment,  concludes  from  it  that  the  sound 
does  not  proceed  from  the  vibrations  of  the  lips;  but  has  its 
origin  in  those  of  the  air,  excited  by  an  intermittent  friction 
against  their  walls.  Longet  and  Masson  compare  the  appar- 
atus for  whistling  in  man  to  the  whistle  of  a  bird-catcher,  and 
they  find  a  close  analogy  between  the  labial  and  the  laryngeal 
glottis. 

Fournie'  rejects  this  theory,  and  supposes  the  sound  of 
whistling  to  be  produced  by  mechanism  analogous  to  that  of 
an  organ-pipe,  the  air  breaking  against  the  stop,  which  is 
represented  by  the  upper  incisors.  Whichever  doctrine  we 
may  accept,  it  is  certain  that  the  lips,  or  the  perforated  disk 
which  replaces  them,  play  an  important  part  in  the  produc- 
tion and  modification  of  sound  in  ordinary  whistling,  for 


238  THE    HUMAN    BODY. 

when  these  sounds  are  made  without  the  aid  of  the  lips,  by 
a  peculiar  disposition  of  the  tongue,  it  is  only  a  single  sound. 
It  is  the  same  in  whistling  through  the  teeth  with  the  lips 
drawn  apart,  or  when  the  tongue  being  doubled,  and  the 
ringers  placed  in  the  mouth,  we  produce  an  intensely  acute 
sound,  but  which  cannot  be  modulated. 

In  the  apparatus  for  whistling,  as  in  that  of  the  voice,  the 
functional  disposition,  and  its  modifications  in  relation  to  the 
sounds  emitted,  takes  place  by  movements  under  the  control 
of  the  will,  although  they  are,  so  to  speak,  instinctive.  The 
changes  in  the  dimensions  of  the  orifices  and  of  the  buccal 
tube,  in  the  tension  of  the  walls  of  the  mouth,  the  impulsion 
of  the  air,  &c.,  are  all  effected  instantaneously,  and  in  such  a 
manner  as  to  produce  all  the  notes.  No  instrument  of  music 
equals  the  perfection  of  this  apparatus. 

Voice. — Voice  is  a  sound  produced  in  the  throat  by  the 
passage  of  the  air  through  the  glottis,  as  it  is  expelled  from 
the  lungs.  It  is  grave  and  strong  in  man,  soft  and  higher  in 
woman;  it  varies  according  to  age,  and  is  developed  simul- 
taneously with  the  larynx,  as  has  already  been  stated.  It  is 
alike  in  both  sexes  in  infancy,  but  is  modified  in  youth;  then 
the  voice  is  said  to  "change."  In  the  young  woman  it  de- 
scends a  note  or  two,  and  becomes  stronger.  In  the  young 
man  the  change  is  much  more  strongly  marked.  At  the 
fourteenth  or  fifteenth  year  the  voice  loses  its  regularity,  be- 
comes harsh  and  unequal,  the  high  notes  cannot  be  sounded, 
while  the  grave  ones  make  their  appearance,  and  the  mascu- 
line character  of  the  voice  is  established.  A  year  is  gene- 
rally sufficient  for  this  change  to  be  complete,  and  the  voice 
of  the  child  gives  place  to  that  of  the  man.  Exercise  of  the 
voice  in  singing  should  be  very  moderate,  if  not  entirely  sus- 
pended, while  this  change  is  going  on. 

Speaking  voice. — Voice  is  divided  into  singing  and  speaking 
voice.  One  differs  from  the  other  almost  as  much  as  noises  do 
from  musical  sounds.  In  speaking,  the  sounds  are  too  short 
to  be  easily  appreciable,  and  are  not  separated  by  fixed  and 
regular  intervals,  like  those  of  singing;  they  are  linked  together 
generally  by  insensible  transitions;  they  are  not  united  by 
the  fixed  relations  of  the  gamut,  and  can  only  be  noted  with 


MECHANISM    OF    ARTICULATE    SOUNDS.  239 

difficulty.  That  it  is  the  short  duration  of  speaking  sounds 
which  distinguishes  them  from  those  of  singing,  is  proved  by 
this,  that  if  we  prolong  the  intonation  of  a  syllable,  or  utter 
it  like  a  note,  the  musical  sound  becomes  evident.  And  if 
we  pronounce  all  the  syllables  of  a  phrase  in  the  same  tone, 
the  speaking  voice  closely  resembles  psalm-singing.  Every 
one  must  have  noticed  this  in  hearing  school-boys  recite  or 
read  in  a  monotone,  and  the  analogy  is  complete  when  the 
last  two  or  three  syllables  are  pronounced  in  a  different  tone. 
Spoken  voice  is  moreover  always  a  chant  more  or  less  marked, 
according  to  the  individual  and  the  sentiment  which  the 
words  express.  The  accentuation  peculiar  to  certain  lan- 
guages also  gives  the  speech  the  character  of  a  chant :  to  a 
French  ear  an  Italian  preacher  seems  always  to  sing.  It  is 
a  chant  also  which  is  caused  by  all  those  inflections  of  the 
voice,  which  express  our  sentiments  and  our  passions,  and 
which  vary  with  every  thought.  They  extend  from  the 
feeble  murmur,  which  the  ear  scarcely  perceives,  to  the 
piercing  cry  of  pain.  Affectionate,  sympathetic,  imperious, 
or  hostile,  they  sometimes  charm,  sometimes  irritate,  and 
always  move  us.  It  is  related  of  Gretry,  that  he  amused 
himself  by  noting  as  exactly  as  possible  the  "Bonjour,  mon- 
sieur!" (Good  day,  sir!)  of  the  persons  who  visited  him;  and 
these  words  expressed  by  their  intonation,  in  fact,  the  most 
opposite  sentiments,  in  spite  of  the  constant  identity  of  the 
literal  sense.  Baron,  the  comedian,  moved  his  audience  to 
tears  by  his  recitation  of  the  stanzas  of  the  song,  "Si  le  roi 
m'avait  donne  Paris  sa  grand* ville" — If  the  king  had  given 
me  Paris  his  great  city. 

Mechanism  of  articulate  sounds. — Writers  are  not  in  accord 
in  explaining  the  pronunciation  of  letters,  that  is,  the  me- 
chanism of  articulate  sounds;  but,  whether  grammarians  or 
physiologists,  they  all  class  the  letters  according  to  the  parts 
of  the  vocal  apparatus  which  co-operate  in  their  pronuncia- 
tion, as  labials,  dentals,  gutterals,  &c.  The  division  of  the 
signs  of  the  alphabet  into  vowels  and  consonants  expresses 
the  universal  idea  that  a  vowel  is  a  voice,  a  sound  perfect  in 
itself,  while  a  consonant  cannot  be  sounded  without  the  help 
of  a  vowel  associated  with  it.  The  consonants,  indeed,  do 


240  THE    HUMAN    BODY. 

not  make  even  a  noise,  a  murmur;  but  they  give  a  peculiar 
character  to  a  vowel  sound.  We  find  something  in  the 
playing  of  an  instrument  analogous  to  this  function  of  a  con- 
sonant. If  we  pinch  the  string  of  a  violin,  or  strike  a  bell 
with  a  hammer,  a  sound  is  produced  which  we  imitate  with 
the  voice  by  prefixing  a  /  or  d,  as  dinn,  tinn;  if  the  string  or 
the  bell  be  made  to  vibrate  with  the  bow,  the  sound  as  re- 
produced by  the  vocal  organ  is  preceded  by  the  letters  cr, 
whence  the  imitative  French  word  crin-criu.  The  hammer 
and  bow  are  the  consonants,  the  note  of  the  bell  or  the  violin 
is  the  vowel. 

Helmholtz  has  demonstrated,  as  we  have  already  observed 
in  speaking  of  hearing,  that  the  timbre  of  sounds  is  deter- 
mined by  the  harmonics.  He  was  able  by  means  of  ingeni- 
ous instruments  to  decompose  the  sounds  which  only  produce 
a  single  sensation,  and  which  seem  to  us  simple,  though  they 
are  really  composed  of  elementary  sounds  more  or  less 
numerous.  This  analysis  enabled  him  to  discover  the  laws 
under  which  the  quality  of  the  sounds  is  constituted  which 
are  emitted  by  the  glottis,  and  resound  in  the  vocal  tube 
under  the  form  of  vowels.  Among  the  elementary  sounds 
composing  the  sound  emitted  by  the  glottis,  the  vocal  tube 
exalts  a  particular  one  by  preference,  and  it  is  this  one 
which  gives  to  the  vowel  its  characteristic  timbre.  The  vocal 
tube  disposes  itself  in  a  special  form  for  each  vowel.  It 
lengthens  or  shortens,  dilates  or  contracts;  it  places  itself,  in 
a  word,  in  conditions  essential  to  the  strengthening  of  the 
sound  which  determines  the  timbre.  Each  vowel  is  there- 
fore characterized  by  a  note,  but  each  one  has  a  particular 
affinity  for  certain  notes;  it  is  sometimes  difficult,  or  even 
impossible,  to  give  such  a  note  on  another  vowel  than  that 
with  which  it  corresponds,  and  thus  singers  are  sometimes 
forced  to  substitute  one  vowel  for  another. 

In  seeking  in  the  different  qualities  of  the  voice,  and 
especially  in  the  vowels,  for  the  seat  of  the  resonance  of 
sounds  in  the  buccal  tube,  and  the  parts  which  co-operate  in 
this  resonance,  Fournie  has  made  a  classification  of  the 
letters,  which  he  claims  to  have  rendered  more  exact  and 
more  anatomical  than  any  of  his  predecessors.  The  tongue, 


THE   VOWELS.       THE    TONGUE    IN    SPEECH.  241 

the  teeth,  the  lips,  and  the  throat,  are  the  parts  by  which 
most  of  the  letters  are  formed.  To  these  Fournie  adds  the 
palate  for  some  of  them,  and  the  glottis  for  the  7z,  which, 
until  recently,  was  classed  among  the  gutturals.  It  is  un- 
necessary to  remark  that  in  the  study  of  the  vowels  in  their 
relation  to  the  mechanism  of  articulate  sounds,  the  laryngo- 
scope has  given  invaluable  aid. 

The  manner  of  forming  the  vowels  differs  from  that  of  the 
consonants  in  this  respect :  the  parts  which  co-operate  in  the 
formation  of  the  vowels  must  be  fixed  during  the  utterance 
of  the  vowel,  while  the  articulation  of  the  consonants  is 
effected  by  a  movement  of  the  parts  essential  to  their  forma- 
tion. Thus  "/,"  is  enunciated  by  suddenly  opening  the  lips 
which  have  been  previously  closed;  and  in  the  same  way 
the  other  consonants  are  pronounced  by  some  movement; 
and  this  movement  is  in  accordance  with  the  disposition  of  the 
parts  necessary  to  the  utterance  of  the  vowel  which  precedes 
or  follows  the  consonant. 

Of  all  the  parts  which  serve  for  the  articulation  of  sounds, 
the  tongue  is  the  one  which  plays  the  principal  part,  and 
therefore  it  gives  its  name  to  the  whole  group  of  modulations 
of  the  voice  which  constitute  language,  or  as  we  sometimes 
say,  a  tongue.  And  yet  observation  teaches  us  that  the 
volume  of  the  tongue  may  be  greatly  diminished,  or  may 
even  exist  only  in  a  rudimentary  state,  without  its  being  im- 
possible to  speak. 

De  Jussieu  relates  that  he  saw  a  girl  fifteen  years  old,  in 
Lisbon,  who  was  born  without  a  tongue,  and  yet  she  spoke  so 
distinctly  as  not  to  excite  the  slightest  suspicion  of  the  ab- 
sence of  that  organ. 

The  Transactions  of  the  Royal  Society  of  London  (1742) 
contain  a  report  of  the  commission  which  was  appointed  to 
investigate  a  case  of  a  similar  nature.  It  was  a  woman 
who  had  not  the  slightest  vestige  of  a  tongue,  but  who  could, 
notwithstanding,  drink,  eat,  and  speak  as  well  and  as  dis- 
tinctly as  any  one,  and  even  articulate  the  words  in  singing. 
Other  instances  have  been  known  where  individuals,  after 
losing  a  portion  of  the  tongue  by  accident  or  disease,  have 
again  been  able  to  speak  after  a  longer  or  shorter  time. 

lo 


242 


THE    HUMAN    BODY. 


Singing. — We  generally  recognize  two  series  of  sounds  in 
the  voice  in  singing,  one  comprising  the  grave  and  semi-acute 
notes,  and  the  other  the  high  notes;  this  is  called  the  register 
of  the  voice,  one  is  the  chest  register  or  voice,  and  the  other 
the  head  register  or  voice,  or  falsetto.  Some  writers  admit  a 
third  series  or  mixed  voice,  which  resembles  a  diminutive 
chest-voice,  in  quality  and  in  the  disposition  of  the  glottis 
when  it  is  produced. 

We  have  indicated  already  the  principal  physiological 
theories  on  the  formation  of  the  voice  in  general:  there  is 
no  less  diversity  in  opinion  in  regard  to  the  falsetto.  Accord- 
ing to  Miiller,  it  results  from  the  vibrations  of  the  edge  only 
of  the  vocal  cords;  other  authors  incline  to  the  notion  that 
the  glottis  no  longer  vibrates  like  a  reed,  but  like  the  mouth- 
piece of  a  flute.  M.  Segond  makes  the  falsetto  voice  to  come 
from  the  superior  glottis  exclusively,  that  is  to  say,  from  the 
vibration  of  the  superior  thyro-arytenoid  ligaments.  This 
opinion  has  been  refuted  by  the  experiments  of  M.  Longet. 
And  lastly,  Weber  and  Longet  attribute  the  origin  of  the 
falsetto  notes  to  the  harmonics  of  the  vocal  cords. 

The  laryngoscope  enables  us  to  study  the  glottis  during 
the  emission  of  the  chest-notes,  and  even  of  the  falsetto 
notes,  but  observers  are  not  agreed  upon  the  phenomena 
which  they  have  observed. 

According  to  Fournie,  the  chest,  the  falsetto,  and  the  mixed 


Fig.  45. — The  glottis  and  vocal  cords. 

A,  E.  Glottis  in  the  chest-voice. 
C.  Glottis  in  thefalse-tto  voice. 


voice,  are  all  produced  by  the  vibration  of  the  mucous  fold 
which  covers  the  free  border  of  the  vocal  corcb. 


CHEST-VOICE.       FALSETTO   VOICE.  243 

In  the  chest-voice  the  larynx  descends  very  low  and  the 
vocal  cords  are  horizontal  and  stretched  simultaneously  in 
length  and  thickness;  the  superior  thyro-arytenoid  ligaments 
project,  and  partly  hide  the  external  border  of  the  vocal 
cords;  the  epiglottis  is  slightly  inclined  over  the  opening  of 
the  larynx;  the  transverse  diameter  of  the  glottis  is  very 
small  and  linear,  and  the  edges  of  the  vocal  cords  are  very 
thick  and  rigid.  The  larynx  rises  in  proportion  as  the  tone 
grows  higher,  the  epiglottis  straightens  again  little  by  little; 
the  plane  of  the  vocal  cords  inclines;  the  orifice  of  the  glottis 
shuts  progressively  from  behind  forward,  and  consequently 
the  vibrating  portions  diminish  in  length,  while  at  the  same 
time  the  tension  increases. 

In  the  falsetto,  the  larynx  is  carried  upward  and  backward 
against  the  spinal  column,  the  soft  palate  rises,  and  its 
posterior  pillars  approach  each  other,  the  ventricles  of  the 
larynx  are  obliterated,  the  vocal  cords  are  wholly  visible,  and 
their  borders  are  in  contact  for  half  their  length  at  least. 
The  glottis  is  therefore  closed  behind,  and  its  orifice,  very 
much  smaller  than  it  was  during  the  utterance  of  the  chest- 
notes,  diminishes  progressively  as  the  notes  grow  higher. 

In  the  mixed  voice  the  glottis  is  open  throughout  its  whole 
length,  and  its  transverse  diameter  is  greater  than  for  the 
other  registers. 

According  to  M.  Battaille,  in  the  chest-voice  the  cords 
vibrate  throughout  their  extent,  the  opening  of  the  glottis  is 
rectilinear,  there  is  less  tension  in  the  walls  of  the  vestibule 
and  glottis,  and  on  the  contrary  more  in  the  vocal  cords, 
than  in  the  falsetto  voice.  In  the  falsetto  voice,  the  arytenoid 
cartilages  embrace  each  other  by  a  sort  of  reversion  in  the 
two  upper  thirds  of  their  internal  surface,  the  glottis  then 
being  ellipsoid  in  form  and  more  open  behind  than  in  the 
chest-voice. 

This  form  of  the  glottis,  which  is  attributed  by  the  eminent 
artist  to  the  falsetto  voice,  is  precisely  the  same  that  M. 
Fournie  has  seen  in  the  mixed  voice,  which  requires  less 
effort. 

M.  Battaille  is  the  only  author  who  notes  the  joining  of 
the  arytenoid  cartilages  by  their  internal  surface:  others 


244  THE    HUMAN    BODY. 

admit  that  they  approach  each  other  at  their  borders  only 
so  as  to  close  the  hollow  which  separates  them  behind,  and 
to  cause  the  vocal  cords  simultaneously  to  face  each  other 
through  part  of  their  length. 

M.  Mandl  has  kindly  communicated  to  us  the  result  of 
his  numerous  observations  on  this  subject;  according  to  his 
opinion,  in  producing  the  chest-voice  the  arytenoid  cartilages 
are  separated  behind;  in  the  falsetto,  in  a  normal  condition,  they 
approach  and  join  each  other  on  their  posterior  border,  which 
causes  the  vocal  cords  to  face  each  other — as  M.  Fournie 
also  says — behind,  while  they  remain  separated  in  front  by 
the  slit  of  the  glottis,  which  has  become  elliptic  and  much 
shorter;  in  certain  persons,  however,  we  observe  something 
analogous  to  the  joining  of  the  arytenoid  cartilages  which 
M.  Battaille  describes,  and  which  belongs  to  the  normal  condi- 
tion of  the  larynx.  In  fact,  when  one  of  these  cartilages  is 
anchylosed  at  its  point  of  union  with  the  cricoid,  and  does 
not  move  to  meet  its  congener,  the  latter  supplies  the  defect 
and  covers  it  by  a  sort  of  overlapping. 

Timbres  (the  distinctive  quality  of  voices). — Besides  that 
quality  which  is  peculiar  to  each  individual,  the  voice  may 
have  several  others,  some  of  which,  as  purity,  are  due  to  the 
perfection  of  the  entire  vocal  apparatus,  and  others,  as  the 
hoarse  nasal  or  guttural  quality,  arise  either  from  the  unskil- 
fulness  of  the  singer  or  from  some  change  in  the  organ. 
There  are  two  forms,  however,  remarkable  because  they  may 
be  produced  at  the  will  of  the  artist,  these  are  the  muffled 
voice  and  the  clear  voice.  Their  names  indicate  their  nature. 
In  the  muffled,  the  sound  is  rounder,  more  velvety,  and  re- 
sembles less  the  sound  of  a  reed;  the  pronunciation  of  the 
letters  is  less  distinct  and  sharp,  and  the  noisy  vowels,  like 
the  a  and  e,  incline  4o  the  timbre  of  o  and  u.  In  the  clear 
voice  the  sound  is  piercing,  somewhat  noisy,  and  less  agree- 
able to  the  ear.  This  high  key  is  more  common  among  the 
northern  nations  of  Europe,  while  the  graver  one  is  ordinarily 
adopted  by  the  singers  of  the  south. 

It  is  generally  admitted  that  the  muffled  voice  is  caused 
principally  by  the  immobility  of  the  larynx  when  as  low  as 
possible,  and  in  fact  the  larynx  is  usually  in  that  position  in 


DIAPASON    OF   VOICES.  245 

singing  in  this  tone :  though  M.  Segond  has  occasionally  seen 
the  larynx  as  high  as  possible  when  this  voice  was  produced. 
This  voice  seems  to  depend  on  the  narrowing  of  the  buccal 
orifice  and  the  isthmus  of  the  throat,  coincident  with  as 
great 'a  dilatation  of  the  mouth  as  possible,  a  disposition 
which  mufiles  and  veils  the  resonance  of  the  sound  in  the 
cavities  of  the  pharynx  and  vocal  tube.  If  in  singing  the 
letter  a,  with  the  mouth  wide  open,  the  lips  be  made  slowly 
to  approach  each  other,  and  pressing  them  together  without 
extending  them,  the  sound  passes  from  the  clear  to  the 
muffled  tone,  and  the  vowel  a  sounds  like  o.  This  move- 
ment of  the  lips  was  very  apparent  in  Mademoiselle  Giulia 
Grisi  in  certain  high  notes,  but  even  her  admirable  voice  was 
insufficient  to  make  us  pardon  her  for  thus  marring  features 
worthy  the  pencil  of  Raphael. 

Diapason  of  voices. — Male  voices  are  divided  into  bass, 
baritone,  or  singing  bass,  and  tenor.  The  voices  of  women 
are  the  contralto,  which  corresponds  to  the  baritone,  mezzo- 
soprano,  and  soprano.  The  extreme  limits  of  these  voices  are, 
for  the  base  the  G  below  the  CC;  for  the  soprano,  the 
F  in  alt.  or  the  F  of  the  last  octave  but  one  of  the  piano.' 
Mozart  heard  a  singer  at  Parma  who  gave  the  C  above. 
Ordinary  voices  do  not  go  beyond  two  octaves,  but  celebrated 
artists  have  compassed  three  and  even  three  and  a  half 
octaves. 

Fortunately  the  prodigious  compass  of  such  a  voice  is  not 
necessary  to  entrance  a  real  lover  of  music.  The  artist  is 
always  sure  to  triumph  when  to  correct  intonation  he  joins 
sympathetic  quality,  and,  what  is  rare,  that  good  taste  which 
will  not  permit  him  to  sacrifice  the  expression  and  the  charac- 
ter of  the  music  to  a  desire  to  shine. 

Instrumental  music  awakens  in  us  the  most  profound 
emotions;  we  are  transported  by  Baillot's  violin  or  the 
orchestra  of  the  Conservatory,  but  no  instrument  can  equal 
the  impression  produced  by  a  beautiful  voice;  no  instrument 
can  pretend  to  those  sounds,  soft  or  sharp,  passionate  or 
purely  peaceful;  none  has  that  variety  in  quality,  those 
accents  which  fascinate  us  and  plunge  us  into  ecstasy.  In- 
struments and  their  voices  are  prodigies  of  art,  but  the  human 


246  THE   HUMAN    BODY. 

voice  is  living  sound,  as  the  glance  of  the  human  eye  is 
animated  light. 

Ventriloquy. — Those  who  created  the  word  ventriloquy 
evidently  believed  in  a  voice  produced  by  some  other  organ 
than  the  larynx.  But  in  these  days  every  one  knows  that 
what  is  called  ventriloquy  consists  in  concealing  the  origin 
and  nature  of  the  voice.  The  ventriloquist  speaks  with  his 
lips  nearly  closed,  and  he  so  modifies  the  sound  of  his  voice 
as  to  make  it  seem  like  that  of  a  child,  or  a  woman;  he 
makes  us  believe  that  it  comes  from  a  chimney  or  a  cavern, 
from  the  far  distance,  from  the  sky,  or  from  the  bowels  of  the 
earth.  In  the  last  century  the  French  Academy  of  Sciences 
appointed  a  commission  to  study  the  phenomena  of  ven- 
triloquy in  a  man  exceedingly  skilful  in  the  art,  but  acting  in 
good  faith  and  making  no  mystery  of  his  power.  It  is  to 
the  uncertainty  as  to  the  direction  of  the  sounds,  and  to  the 
errors  into  which  we  are  easily  led  by  the  organ  of  hearing, 
more  than  to  anything  else,  that  the  ventriloquist  owes  his 
success.  They  may  deceive  ignorant  and  credulous  people, 
but  they  are  generally  content  to  amuse  their  auditory,  and 
in  that  they  succeed. 


CHAPTER  XVII. 


Physiognomy;  study  of  it  in  works  of  art. — Movements  of  expression,  their 
seat. — Colouring  of  the  skin;  paleness,  redness. — Expression  of  the 
muscles;  effort,  muscles  of  the  face. — Physiognomy  of  the  senses. — Ex- 
pression of  the  eyes,  vision,  easy  or  difficult,  blindness.  — Expression  in 
the  act  of  hearing,  easy  or  difficult,  hearing  of  an  orator,  musical  hear- 
ing. — Expressions  of  smell  and  t.iste. — Expressions  relating  to  the  touch. 


Physiognomy  is  generally  considered  as  the  expression  of 
the  features  of  the  face,  but  it  is  not  so  limited  in  its  elements. 
Attitude,  repose  or  action,  fulness  or  slenderness  of  form, 
proportion,  bold  or  graceful  relief,  and  lastly,  health  or 
disease  have,  in  the  entire  contour  of  the  body,  a  significa- 
tion which  completes  that  of  the  face.  Physiognomy,  there- 
fore, is  the  expression  which  form  and  motion  give  to  the 
body. 

In  the  Caryatides  of  the  temple  of  Erectheus,  we  admire 
the  calmness  and  grandeur,  the  majesty  of  the  draperies,  the 
simple  and  grave  lines  of  the  figures  which  support  without 
effort  the  marble  that  seems  not  to  weigh  upon  them.  In 
the  Caryatides  of  Puget  at  Toulon,  we  see  the  display  of 
power  in  the  violently  contracted  muscles,  in  the  arms  which 
seek  to  relieve  the  head  from  the  burden,  under  which  the 
whole  body  stiffens,  and  is  about  to  succumb ! 

Compare  a  Silenus  to  the  Farnese  Hercules.  In  the  old 
friend  of  Bacchus,  the  form  is  heavy,  obese,  and  flaccid;  it  is 
the  abjectness  of  drunkenness;  in  the  other,  the  powerful 
muscles,  the  firm  proud  attitude,  the  noble  bearing,  declare 
the  tamer  of  monsters  and  of  vices.  The  Diana  Huntress, 
with  her  sure  and  rapid  step,  is  the  enemy  of  idleness  and 
repose ;  her  manner  is  severe,  and  human  passion  has  never 


248  THE    HUMAN    BODY. 

throbbed  in  her  virgin  breast.  The  Venus  Anadyomene, 
graceful,  timid,  uncertain  in  manner,  shows  much  more  of 
feeble  humanity. 

It  is  to  this  profound  sense  of  physiognomy  in  the  great 
artists  that  we  owe  the  lively  emotion  which  the  sight  of  their 
master-pieces  produces,  and  the  ancients  do  not,  in  our  judg- 
ment, merit  the  reproach  cast  upon  them  for  the  want  of 
expression  in  their  heads. 

The  Greeks,  for  whom  statuary  was  especially  a  monu- 
mental art,  gave*  to  their  faces  the  calm  and  dignity  of  gods, 
rather  than  human  passions;  therefore  the  action  was  quiet, 
the  lines  simple,  and  the  expression  of  the  head  in  harmony 
with  that  of  the  body;  but  when  they  turned  to  dramatic 
subjects,  the  few  examples  which  remain  enable  us  to  judge 
that  they  were  not  less  admirable  in  works  of  this  nature. 

They  no  doubt  guarded  against  empty  grimaces,  and  it 
was  principally  in  action  that  they  placed  the  expression; 
but  can  we  not  read  disdainful  anger  on  Apollo's  lip?  and 
is  not  pride  stamped  on  the  features  of  the  Venus  of  Milo? 
does  not  watchfulness  careless  of  danger  look  from  the  eyes 
of  the  Gladiator,  and  love,  almost  paternal,  rest  on  the  simple, 
spiritual  head  of  the  Faun  and  Child?  Do  we  not  feel  a 
mother's  pain  in  the  Niobe,  see  the  suffering  and  the  prayer 
in  the  look  of  the  Laocoon?  The  sculptors  of  the  Renais- 
sance imposed  the  same  rule  upon  themselves  before  the 
works  of  antiquity  were  revealed  to  them.  They  were  fol- 
lowed also  by  the  painters,  although  for  them  these  rules 
were  less  inflexible,  and  yielded  more  to  details  in  an  art 
more  nearly  allied  to  living  nature. 

The  artist  finds  in  anatomical  physiology,  and  in  physi- 
ognomy, useful  hints  and  precise  principles;  but  he  rightly 
abstains  from  a  rigorous  and  servile  application  of  them, 
for  though  the  physician  may  find  it  important  to  know 
the  exact  function  of  a  certain  muscle,  the  sculptor  and 
the  painter  must  confine  himself  to  the  true  but  not  realistic 
expression  caused  by  its  contraction.  To  go  beyond  this, 
which  is  very  easy,  is  to  arrive  at  that  repugnant  reality  which 
certain  masters  of  the  Spanish  school  have  not  hesitated  to 
adopt. 


MOVEMENTS    OF    EXPRESSION.  249 

Caught  from  nature  by  photography,  physiological  expres- 
sion belongs  to  science,  and  is  invaluable  to  it:  but  the  artist, 
like  the  poet,  remembers  that  his  task  is  to  suggest  only, 
leaving  that  to  be  divined  which  could  not  be  said  or  de- 
lineated without  revolting  the  spectator. 

The  movements  from  which  the  physiognomy  results  are 
always  harmonious,  and  it  is  to  their  unity  and  concordance 
that  our  impressions  are  due.  The  least  negligence  in  this 
respect  shocks  us  in  a  picture  like  a  false  note  in  an  orchestra, 
while  our  admiration  is  unbounded  for  a  work  of  art  in  which 
nothing  is  forgotten. 

Lethiere  paints  Brutus  at  the  execution  of  his  sons;  the  face 
and  attitude  of  the  consul  express  only  merciless  severity,  the 
folds  of  the  toga  are  faultless,  but  the  contracted  hands 
reveal  the  agony  of  the  father  under  the  inflexibility  of  the 
judge.  David  represents  him  to  us  at  the  moment  when  the 
bodies  of  his  sons  are  brought  to  him.  The  expression  of 
the  head  is  fierce,  the  feet,  the  left  hand,  and  the  whole  body 
are  strongly  contracted;  the  right  hand  alone  is  carelessly 
bent,  and  takes  no  part  in  this  convulsive  state. 

Movements  of  expression. — Gratiolet,  in  his  treatise  on 
physiognomy,  groups  under  this  term  all  the  modifications  of 
form,  of  colour,  &c.,  which  manifest  themselves  on  the  sur- 
face of  the  body,  under  the  influence  of  the  most  widely  dif- 
ferent causes.  These  movements  are  direct,  sympathetic,  or 
symbolic. 

In  looking  at  an  object,  the  action  of  the  eyes,  and  the 
animation  which  they  give  to  the  expression,  are  direct  move- 
ments; but  if  we  fix  the  attention,  the  body  takes  part  in  the 
action  of  the  eyes,  inclines  forward,  and  seems  to  wish  to 
move  toward  the  object  observed;  these  are  sympathetic 
movements,  and  when  thinking  of  extreme  cold  we  shiver, 
this  is  a  symbolic  movement. 

The  limbs,  the  trunk,  and  the  head,  that  is  to  say,  the 
gestures  and  attitude,  contribute  greatly  to  complete  the 
physiognomy,  as  has  already  been  remarked ;  the  cavities,  on 
the  contrary,  take  no  part  in  it,  the  seat  of  expression  is  in 
the  skin,  the  muscles,  and  the  eyes. 

Colour  of  the  integuments. — The  skin,  parti cularlv  on  the 


250  THE    HUMAN    BODY. 

face,  takes  the  greatest  variety  of  tints,  from  a  violet  red  to  a 
livid  pallor,  under  the  influence  of  physical  or  moral  causes, 
which  quicken  or  retard  the  circulation  of  the  blood;  but 
besides  the  colouring  of  the  face,  it  is  the  movement  of  the 
muscles,  and  the  expression  of  the  eyes,  which  gives  it  a 
definite  signification. 

In  a  feeble  man  the  motion  of  the  heart  is  retarded,  or 
sometimes  hurried,  as  if  to  make  up  in  the  number  of  its 
beats  for  their  want  of  energy;  the  blood  is  not  sent  to  the 
surface  in  sufficient  quantity,  and  the  face  is  pale;  but  the 
languor  of  form  and  look  denote  the  cause  of  the  pallor. 

Cold  causes  contraction  of  the  tissues,  the  circulation  is 
impeded  on  the  surface  of  the  body,  the  features  seem 
pinched,  the  lips,  nose,  and  cheeks  take  a  livid  leaden  hue; 
chills  sometimes  shake  the  limbs  and  the  lower  jaw;  on  the 
face,  as  well  as  over  the  whole  body,  the  integument  is  the 
seat  of  a  painful  constriction,  but  the  eyes  only  express  suf- 
fering. When  an  assassin  reproached  Bailly  with  being 
afraid,  he  replied,  "No,  my  friend,  I  am  cold." 

Violent  exercise,  joy,  confusion,  fury,  all  quicken  the 
action  of  the  heart,  and  precipitate  the  movement  of  the 
blood  through  the  teguments,  which  relax  or  yield  to  the 
impulsion  of  the  fluid;  but  the  open  mouth,  the  dilated 
nostrils,  the  heaving  chest,  the  strong  and  rapid  respiration, 
express,  as  well  as  the  features,  an  agitation  purely  physical, 
and  we  are  not  tempted  to  assign  a  moral  cause  for  the  flush 
which  follows  muscular  effort.  The  serenity  and  expansion 
of  the  features,  the  smile,  the  brightness  and  happiness  ex- 
pressed in  the  eye  when  the  face  is  flushed  with  joy,  have 
nothing  in  common  with  the  downcast  eyes,  the  falling  lip, 
the  muscular  weakness,  and  embarrassed  manner  of  the  man 
who  reddens  with  confusion.  We  easily  recognize  also  the 
haggard  and  threatening  eyes,  the  knitted  brow,  the  com- 
pressed lips,  and  the  violently  contracted  or  strongly  agitated 
muscles  of  a  man  who  is  a  prey  to  anger,  and  in  whom  the 
blood,  at  first  impeded  in  its  course,  now  in  its  reaction 
forcibly  injects  the  integuments. 

We  see  by  these  few  examples  that  the  colouring  of  the 
skin,  varying  under  the  influence  of  the  most  diverse  causes, 


EXPRESSION    OF    THE    MUSCLES.  251 

is  an  important  element  in  physiognomy,  though  its  significa- 
tion is  doubtful,  and  must  be  completed  by  the  expression  of 
all  the  other  features,  or  of  the  body. 

Expression  of  the  muscles. — The  action  of  the  muscles  and 
the  movements  resulting  from  it,  have,  on  the  contrary,  a 
special  character,  whether  taken  as  a  whole  or  individually, 
in  certain  muscles  of  the  face.  In  making  an  effort,  these 
movements  embrace  the  whole  muscular  system,  and  the 
expression  which  results  is  more  characteristic.  When  re- 
produced by  the  plastic  arts,  it  strongly  impresses  the  spec- 
tator, who  feels  a  sort  of  sympathetic  contraction,  but  which 
soon  fatigues  and  irritates  like  all  inconstant  attitudes. 

The  muscles  of  the  face  by  their  single  or  combined  con- 
traction cause  the  most  widely  differing  expressions,  and 
correspond  to  all  the  sentiments,  whether  simple  or  complex. 
Thus,  the  muscle  of  the  forehead  raises  the  brow  in  attention, 
admiration,  or  astonishment;  that  of  the  eyebrow  contracts 
it  with  pain ;  the  great  zygomatic  raises  the  angle  of  the  lips 
in  laughing;  the  triangular  muscle  of  the  lips  draws  them 
downward  in  weeping;  other  muscles  co-operate  in  expres- 
sing combativeness,  fear,  anger,  irony,  &c.,  in  short,  the 
slightest  phase  of  feeling  is  reproduced  in  the  features,  by 
the  slight  or  energetic  contractions  of  the  muscles,  which 
carry  with  them  the  skin  to  which  they  are  intimately  united, 
wrinkling  or  distending  it.  An  eminent  physiologist,  M. 
Duchenne  of  Boulogne,  particularized  the  action  of  these 
muscles  in  expressive  movements.  But  though  some  of 
them  may  play  a  distinct  part  in  the  mimicry  of  the  face, 
others  always  join  in  the  movements  when  the  sentiment  or 
sensation  acquires  a  certain  vivacity;  thus  the  muscle  of  the 
eyebrow  alone  may  express  a  certain  degree  of  suffering,  but 
when  it  becomes  intense  the  eyelids  close,  the  nostrils  dilate, 
and  other  signs  beside  prove  the  simultaneous  action  of  the 
different  muscles.  For  the  physiologist  and  the  physician, 
rigorously  exact  facts  of  this  sort  have  the  greatest  value; 
but  they  are  of  less  consequence  to  the  artist,  who  must  repre- 
sent not  only  the  muscle  but  the  whole  of  the  parts,  near  or 
distant,  to  which  its  action  extends.  If  it  is  necessary  for 
him  to  understand  anatomy  and  the  function  of  the  muscles 


252  THE    HUMAN    BODY. 

in  order  to  reproduce  exactly  their  projection  during  move- 
ments of  the  body  and  limbs,  it  is  much  more  the  study  of 
the  living  model  which  guides  him  when  endeavouring  to 
render  the  expression  of  the  features;  and  if  he  fails  in  this, 
it  is  less  from  ignorance  of  anatomy  than  from  lack  of  senti- 
ment or  incapacity. 

It  is  remarkable  also  how  much  opinion  varies  in  regard 
to  works  of  art.  Each  individual  brings  to  their  examination 
the  predisposition  of  his  studies;  and  if  the  naturalist  may 
sometimes  criticize  justly,  sometimes  also  in  his  judgments 
the  artistic  sentiment  is  replaced  by  the  rigorous  formulas 
and  exact  notions  of  science;  he  does  not  consider  that  the 
artist  should  avoid  being  as  exact  as  a  Chinese  copy,  anci 
that  a  profound  artistic  sentiment  should  be  completed  in 
its  expression  by  its'  counterpart  in  the  spectator.  And  lastly, 
a  savant  may  be  a  man  of  genius,  and  still  lack  all  artistic 
sentiment.  Gratiolet,  that  fine  and  noble  mind,  could  see 
nothing  in  Raphael's  "Creation"  but  a  "deplorable  work — a 
furious  old  man  striving  with  feet  and  hands  to  separate  two 
thick  clouds."  The  man  who  criticized  one  of  the  most 
admirable  master-pieces  of  art  in  these  terms,  was  a  scholar 
of  the  first  order,  a  great  physiologist,  and  has  left  a  wrork 
on  physiognomy  itself  marked  by  the  most  delicate  percep- 
tions and  the  most  profound  study. 

Physiognomy  of  the  senses. — The  more  the  mind  predomin- 
ates over  matter,  and  separates  itself  from  it,  the  more  elevated 
will  be  the  expression  of  the  physiognomy.  Faith  and 
prayer  transport  man  into  an  order  of  ideas  purely  intellec- 
tual, and  give  to  the  features  a  character  in  which  sense  has 
no  part.  Resignation  attaches  itself  to  the  terrestrial  affec- 
tions, and  mingles  with  them  an  element  of  pain  which, 
whether  moral  or  physical,  is  always  expressed  by  the  marks 
of  suffering.  The  recital  of  a  dishonourable  action  adds  a 
shade  of  disgust  to  indignation,  and  the  moral  impression 
seems  to  affect  our  organs  as  they  are  affected  by  material 
impressions. 

This  indirect  and,  as  it  were,  figurative  action  of  the  senses 
on  the  physiognomy,  mingles  incessantly  with  movements  of 
another  order,  and  often  expresses  itself  with  as  much  energy 


EXPRESSION    OF    THE    EYE.  253 

as  the  real  sensations.  When  these  latter  are  acute  they 
govern  the  expression  almost  as  completely  as  the  most 
violent  passions,  and  may,  like  them,  impress  upon  the 
features  the  sign  of  an  infirmity,  a  fault,  or  a  vice. 

Our  senses,  as  has  been  already  stated,  are  united  by  the 
constant  relations  of  complementary  or  sympathetic  functions, 
as  the  sight  and  the  touch,  the  sight  and  the  hearing,  the 
taste  and  the  smell  frequently  control  or  complete  each  other 
by  their  simultaneous  action,  and  often  all  the  senses  are  in 
action  at  once.  This  coincidence  of  the  sensations  reflected 
by  the  physiognomy  is  a  source  of  varied  and  complex  expres- 
sions, as  much  so  as  the  nervous  impressions  transmitted  to 
the  brain  can  be,  and  to  describe  the  physiognomy  of  any 
one  sense  it  is  necessary  almost  to  draw  all  the  features  of 
each  of  the  other  senses. 

The  eye  gives  an  expression  of  intelligence  to  the  physiog- 
nomy, and  reflects  the  thought  more  than  any  other  organ  of 
the  senses.  It  is  especially  through  the  eye  that  the  passions 
reveal  themselves — that  joy  or  sorrow,  courage  or  fear,  envy, 
love,  or  hate,  frankness  or  duplicity,  are  expressed  on  the 
features;  therefore,  says  one,  if  you  would  know  a  man's 
sentiments,  read  them  in  his  eyes. 

The  movements  of  the  globe  of  the  eye,  its  fixity,  and  the 
contraction  or  dilatation  of  the  pupil,  infinitely  vary  the  ex- 
pression of  the  face,  and  give  to  the  whole  of  the  features  a 
decided  meaning;  but  to  the  mimic  language  of  the  globe 
the  eyelids  bring  an  important  and  often  decisive  addition. 

When  sight  is  good,  attention  is  expressed  without  effort: 
the  face  is  calm;  the  eyelids,  moderately  open,  show  the  globe 
of  the  eye,  which  fixes  itself  on  the  object,  follows  it  in  space, 
and  acts,  in  short,  as  do  all  the  organs  in  a  normal  condi- 
tion, without  any  consciousness;  but  if,  on  the  contrary,  it 
is  necessary  to  distinguish  an  object  which  is  perceived  with 
difficulty,  the  eyelids  approach  each  other,  the  eyes  twinkle, 
and  the  immobility  of  the  body,  the  suspended  respiration", 
denote  more  marked  attention;  the  brow  contracts,  and  the 
features  wear  an  expression  of  pain,  which  sometimes  gives 
short-sighted  persons  a  forbidding  character. 

The  face  of  a  blind  man  is  rarely  sad,  but  the  immobility 


254  THE    HUMAN    BODY. 

of  the  features,  which  are  so  animated  by  vision,  produces  a 
painful  contrast. 

In  hearing  the  attention  is  also  more  or  less  characteristic. 
If  we  wish  to  distinguish  a  distant  noise,  or  perceive  a  sound, 
the  head  inclines  and  turns  in  such  a  manner  as  to  present 
the  external  ear  in  the  direction  of  the  sound,  at  the  same 
time  the  eyes  are  fixed  and  partially  closed.  The  movement 
of  the  lips  of  his  interlocutor  is  the  usual  means  by  which 
the  deaf  man  supplies  the  want  of  hearing;  the  eyes  and  the 
entire  head,  from  its  position,  have  a  peculiar  and  painful 
expression  of  attention.  In  looking  at  the  portrait  of  La 
Condamine  it  was  easily  recognized  as  that  of  a  deaf  person. 
Even  when  hearing  is  perfect  the  eyes  act  sometimes  as 
auxiliaries  to  it;  in  order  to  understand  an  orator  perfectly, 
it  seems  necessary  to  see  him — the  gestures  and  the  expres- 
sion of  the  face  seem  to  add  to  the  clearness  of  the  words. 
The  lesson  of  a  teacher  cannot  be  well  understood  if  any 
obstacle  is  interposed  between  him  and  the  eyes  of  the  listen- 
ing pupil. 

That  species  of  intoxication  which  we  term  ecstasy  is  ex- 
pressed on  the  features  of  a  musical  amateur  on  hearing  a 
master-piece;  all  the  powers  of  attention  are  concentrated  on 
one  organ;  the  features  are  slightly  contracted  by  the  smile 
or  other  expression  in  accordance  with  the  character  of  the 
music;  the  eyes  are  half  shut  or  closed,  though  sometimes 
they  are  fixed  agonizingly  on  the  singer  in  some  difficult  pas- 
sage, or  enthusiastically  on  some  leader,  like  Habeneck, 
leading  his  orchestra  with  a  passionate  gesture. 

If  a  piercing,  harsh,  or  discordant  sound  strikes  the  car, 
the  eyes  close,  and  at  the  same  time  the  lips,  the  nose,  and 
the  whole  face  contract  as  if  the  other  senses  were  combining 
to  protect  the  hearing  from  the  pain  it  endures,  and  against 
which  its  immovable  organ  cannot  defend  it.  It  is  impatient 
suffering,  and  no  longer  the  charm  of  a  delicious  sensation. 

Under  the  influence  of  the  smell  and  the  taste  the  expres- 
sion of  the  physiognomy  is  extremely  varied,  and  reflects 
perfectly  the  delicacy  or  the  force  of  the  sensation,  the 
degree  of  pleasure  which  accompanies  it,  or  the  horror  and 
repugnance  which  it  excites  in  us.  Here,  as  in  hearing, 


EXPRESSION    OF    TOUCH.  255 

sympathetic  movements  are  combined  with  the  direct  move- 
ments produced  in  the  affected  organs.  When  taste  is  con- 
cerned, it  is  very  rare  that  they  are  not  confounded,  for 
almost  always  the  aroma  is  combined  with  the  taste,  and 
either  perfects  its  excellence  or  renders  it  still  more  insup- 
portable. But  whether  it  expresses  satisfaction  or  antipathy, 
the  play  of  the  physiognomy  in  sensations  of  this  nature  has 
nothing  elevated  in  it,  rather  it  unveils  a  certain  abasement 
of  the  individual;  hearing  and  sight  are  in  immediate  con- 
nection with  the  most  precious  faculties  of  the  mind,  while 
taste  and  smell  appeal  specially  and  directly  to  our  material 
appetites.  But  we  must  not  therefore  judge  too  severely  the 
elation- of  a  gourmand  seated  at  a  well-spread  table.  The 
best  compliment  he  can  oifer  to  his  host  is  to  show  a  worthy 
appreciation  of  an  exquisite  repast.  We  shall  see  the  spirit 
of  our  guest,  vivified  by  the  sweet  influence,  shine  from  his 
eyes  with  a  light  which  will  easily  enable  us  to  pardon  what 
little  of  sensuality  there  is  in  his  mouth. 

It  is  by  the  sense  of  touch  that  we  acquire  clear  ideas  of  the 
form  of  bodies,  of  the  distance,  resistance,  weight,  tempera- 
ture, &c.  It  confirms  the  testimony  of  our  eyes,  and  joins 
its  impressions  to  those  of  sight  often  in  an  effective  manner, 
and  always  through  the  mind. 

The  touch  produces  expressive  movements  in  us  then,  in 
connection  with  our  tactile  or  visual  sensations;  and  these 
movements  are  sometimes  direct,  as  in  effort,  and  sometimes 
sympathetic  and  an  indication  of  the  impressions  produced 
on  the  skin.  Lastly,  touch  is  the  origin  of  symbolical  move- 
ments by  which  we  express  the  thought  of  bringing  an  ob- 
ject near,  or  putting  it  away  from  us.  To  this  sense  are  re- 
lated the  gestures  which  accompany  our  words.  WTe  affirm 
a  fact  by  so  placing  the  hand  as  if  we  would  rest  it  firmly  on 
a  body;  we  deny  by  a  gesture  putting  the  false  or  erroneous 
proposition  away  from  us;  we  express  doubt  by  holding  the 
hand  suspended,  as  if  hesitating  whether  to  take  or  reject. 
When  we  part  from  dear  friends,  or  greet  them  again  after 
long  absence,  the  hand  extends  towards  them  as  if  to  retain, 
or  to  bring  them  sooner  to  us.  If  a  recital  or  a  proposition 
is  revolting,  we  reject  it  energetically  in  gesture  as  in  thought. 


256  THE    HUMAN    BODY. 

In  a  friendly  adieu  we  wave  our  good  wishes  through  space 
to  him  who  is  the  object  of  them;  but  when  it  expresses 
enmity,  by  a  brusque  movement  we  sever  every  tie.  The 
open  hand  is  carried  backward  to  express  fear  or  horror,  as 
well  as  to  avoid  contact;  it  goes  forward  to  meet  the  hand  of 
friendship;  it  is  raised  suppliantly  in  prayer  toward  Him 
from  whom  we  hope  for  help;  it  caresses  lovingly  the  downy 
cheek  of  the  infant,  and  rests  on  its  head  invoking  the  bless- 
ing of  Heaven;  in  a  word,  the  touch,  real  or  imaginary,  is 
constantly  adding  a  feature  to  the  physiognomy. 


THE   END, 


642-2531 


LePilaur. 
wonaers 
bodv. 

3f  the  human 

QF34 
L36 

uvu^  , 

BIOLOGY 
LIBRARY 

G 

\     ";     G 

Aug.  31  f  16 

Holmes    ^ 

.   ' 

L  9  U 

^ 

70^ 

UEFARY 


34 


THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


